UC-NRLF 


'fiicago    Nature-Study    Series 


am 


FIELD  AND   LABORATORY 
.  GUIDE  IN  PHYSICAL 

NATURE-STUDY 


ELLIOT  R.  DOWNING 

sociate  Professor  of  Natural  Science  in  tl 

Ec'ucaticm  of  the  University  of  Chicago 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


A  FIELD  AND  LABORATORY  GUIDE 
IN  PHYSICAL  NATURE-STUDY 


"V) 


PREFACE 


It  is  unfortunate  that  the  term  "nature-study"  has  come  to  connote 
experience  with  living  things  chiefly  and  that  in  practice  the  nature-study 
work  largely  neglects  that  rich  field  of  physical  science  that  lies  so  close  to 
the  child,  the  stars  that  stimulate  his  wonder,  the  rocks  and  minerals 
which  he  collects  with  such  delight,  the  toys  and  home  appliances  from 
which  he  may  obtain  such  a  wealth  of  useful  experience  that  will  clarify 
in  his  mind  fundamental  science  concepts.  The  present  volume  attempts 
to  organize  this  more  or  less  neglected  material  for  the  use  of  the  teacher. 

The  author  has  used  the  material  here  presented  with  his  own  teacher- 
training  classes  for  many  years.  It  is  in  the  hope  that  it  will  serve  normal- 
school  teachers  who  are  also  preparing  pupils  to  teach  nature-study  in  the 
grades  that  the  book  is  published.  If  a  short  title  were  given  to  the  book 
it  might  well  be  "How  to  Make"  as  the  companion  volume,  The  Field  and 
Laboratory  Guide  in  Biological  Nature-Study,  might  be  designated  "What  to 
See."  I  can  do  no  better  than  repeat  here  the  sentiment  expressed  in  the 
Preface  to  the  preceding  volume.  It  is  expected  that  the  book  will  prove 
helpful  to  that  large  and  increasing  group  of  teachers,  both  actual  and 
prospective,  who  are  earnestly  trying  to  use  in  the  schools  that  scientific 
method  and  accumulated  knowledge  so  important  in  modern  life.  Further- 
more, it  is  hoped  that  through  the  teachers  it  will  serve  those  boys  and  girls 
who,  by  acquaintance  with  nature,  will  come  to  adjust  themselves  more 
intelligently  to  their  environment,  use  the  forces  of  the  universe  more 
effectively,  and  be  happier  in  their  enlarged  outlook. 

ELLIOT  R.  DOWNING 
THE  UNIVERSITY  OF  CHICAGO 
THE  SCHOOL  OF  EDUCATION 
September  29,  1919 


CONTENTS 

PAGE 

INTRODUCTION 5 

COMMON  MINERALS  AND  ROCKS    .       . -6 

THE  STARS  AND  OUR  SOLAR  SYSTEM .       .       15 

SOME  TOYS  THAT  WORK  BY  AIR 28 

TOP,  SLING,  AND  Bow     .       .       . .       .43 

THE  HOT-AIR  BALLOON  AND  SOME  EXPERIMENTS  TO  SHOW   How   IT 

WORKS 51 

SOME  COMMON  APPLIANCES  THAT  OPERATE  BY  HEAT 56 

MAGNETIC  AND  ELECTRIC  TOYS 67 

THE  CAMERA,  TELESCOPE,  MAGIC  LANTERN,  AND  SOME  EXPERIMENTS  IN 

LIGHT 81 

THE  HOMEMADE  ORCHESTRA 90 

How  TO  MAKE  THE  PHONOGRAPH  AND  TELEPHONE  .       .,      .       .       .       .      95 

How  TO  MAKE  A  PAIR  OF  SCALES  AND  USE  OTHER  MECHANICAL  CON- 
TRIVANCES  101 

APPENDIX 103 


415689 


INTRODUCTION 

Look  over  some  good  courses  of  study  in  nature-study  to  see  that 
you  will  be  expected  as  a  teacher  to  lead  pupils  into  those  experiences  that 
give  them  contact  with  essential  scientific  facts  and  phenomena.  If  pos- 
sible visit  nature-study  classes  so  that  you  may  see  that  the  sort  of  thing 
here  presented  is  what  you  will  need  when  as  a  teacher  you  face  actual 
schoolroom  work. 

Before  the  pupil  has  completed  the  junior  high  school  he  should  be 
assured  of  a  range  of  experience  with  commonplace  science  that  will  habit- 
uate him  to  see  and  to  attempt  the  solution  of  problems  in  a  scientific 
way,  that  will  give  him  command  of  the  most  important  principles  of  science 
and  that  will  make  him  appreciative  of  the  wonders  to  be  found  in  his 
commonplace  environment.  This  book  attempts  to  prepare  the  teacher 
to  intelligently  use  the  physical  materials  of  interest  to  the  pupil  to  achieve 
such  ends. 

It  is  suggested  that  not  all  of  the  projects  outlined  be  undertaken  by 
each  student-teacher  but  that  some  be  assigned  to  particular  students  to 
work  out  before  the  class  or  undertaken  by  the  instructor  as  class  demon- 
strations. The  author  suggests  from  his  experience  in  handling  this  work 
that  the  projects  listed  in  the  Appendix  be  so  assigned  and  that  the  remain- 
ing ones  be  done  by  each  student  of  the  class.  There  is  also  given  in  the 
Appendix  an  estimate  of  the  apparatus  required  for  the  course  on  the 
foregoing  basis  with  a  class  of  twenty  students. 

All  projects  are  to  be  written  up  by  the  individual  student  as  if  performed 
by  himself,  so  that  each  one  may  feel  responsible  for  those  done  for  him, 
to  save  time,  by  other  members  of  the  class.  Write  up  the  notes  as  directed 
in  ink  on  the  blank  pages  provided,  answering  all  questions  asked.  Make 
such  diagrams  and  sketches  as  are  called  for,  also  in  ink,  preferably  Hig- 
gins'  water-proof  drawing  ink. 

Follow  carefully  the  directions  given  for  making  and  operating  the 
appliances  and  toys.  Put  yourself  as  far  as  possible  in  the  place  of  the 
child  who  is  having  these  experiences.  See  in  them  the  problems  he  would 
see  and  think  them  through  on  the  basis  of  your  own  observations.  It  is 
more  important  that  you  cultivate  the  scientific  attitude  of  mind  than  that 
you  amass  much  information.  Be  neat,  accurate,  and  thoroughgoing  in 
your  work;  cultivate  a  workman-like  pride  in  the  product  of  your  own 
handwork. 


COMMON  MINERALS  AND  ROCKS 

The  collection. — i.  Make  two  cardboard,  wooden,  or  tin  trays,  each  with 
thirty-six  compartments,  2  by  3  inches  and  2\  inches  deep,  to  hold  your 
minerals  and  rocks.  Obtain  from  some  dealer,  like  Ward's  Natural  History 
Establishment,  at  Rochester,  New  York  (or  collect  for  yourself),  the 
following  minerals  and  rocks  for  study. 

Minerals. — Amphibole  or  hornblende  both  (i)  massive  and  (2)  crystal- 
lized; (3)  apatite;  augite  or  pyroxene,  both  (4)  massive  and  (5)  crys- 
tallized; calcite  (6)  massive  and  (7)  crystallized  as  dogtooth  spar;  (8) 
chalcopyrite;  (9)  chalk;  (10)  chlorite;  (n)  corundum;  (12)  dolomite  or  heavy 
spar;  feldspar  is  the  name  of  a  family  of  minerals  including  (13)  orthoclase 
and  several  plagioclases,  such  as  (14)  albite,  (15)  anorthite,  (16)  oligoclase, 
(17)  labradorite;  (18)  fluorite;  (19)  galenite;  when  massive  gypsum  is 
called  (20)  alabastine  if  clean  and  fine-grained,  (21)  selenite  when  crystal- 
lized; (22)  hematite;  (23)  kaolin;  (24)  limonite;  (25)  malachite;  mica  both 
(26)  biotite  and  (27)  muscovite;  (28)  olivine;  (29)  pyrite,  crystallized; 
quartz  occurs  in  a  variety  of  forms  (30)  massive,  (31)  crystal,  (32)  agate, 
(33)  amethyst,  (34)  chalcedony,  (35)  flint,  (36)  jasper,  (37)  rose  quartz; 
(38)  serpentine;  (39)  sphalerite;  (40)  tin  ore,  cassiterite. 

Rocks. — {i)  Amygdaloid  of  copper;  (2)  andesite;  (3)  basalt;  (4)  breccia; 
(5)  conglomerate;  (6)  diabase  and  (7)  olivine  diabase;  (8)  diorite  and  (9) 
porphyritic  diorite;  (10)  gabbro;  (n)  gneiss;  (12)  granite  and  both  (13) 
biotite  and  (14)  hornblende  granite;  (15)  limestone  and  (16)  fossiliferous 
limestone;  (17)  marble  and  (18)  dolomitic  marble;  (19)  obsidian;  (20) 
pumice;  (21)  quartzite;  (22)  sandstone;  schist  both  (23)  chloritic  and  (24) 
micaceous;  (25)  syenite;  (26)  shale;  (27)  slate. 

The  school  may  provide  these  type  minerals  and  rocks  for  study  and 
the  pupils  may  use  the  trays  for  local  collections  properly  labeled. 

Characteristics  of  minerals. — -Define  (opposite  page)  a  mineral.  Define 
a  rock.  Minerals  are  distinguished  by  several  characteristics.  They  crystal- 
lize in  definite  shapes.  Study  a  crystal  of  quartz.  Note  that  it  is  a  six- 
sided  prism  with  a  six-sided  pyramid  at  each  end  (if  perfect).  Note  the 
cubical  or  dodecahedral  crystals  of  iron  pyrite. 

2.  Melt  some  sulphur  in  an  evaporating  dish  over  the  Bunsen  burner. 
Let  it  cool  until  it  begins  to  solidify  about  the  edges.  Then  pour  out  most 
of  it  and  what  is  left  will  set  in  crystal  form.  What  is  the  shape  of  the 
crystals? 


COMMON  MINERALS  AND  ROCKS  7 

3.  Make  a  strong  solution  of  alum  in  hot  water.  Let  it  stand  in  an 
open  dish  so  that  the  water  will  evaporate.  The  alum  will  deposit  in 
crystal  form. 

Many  minerals  split  easily  along  certain  planes  so  that  the  fragments 
are  bounded  by  smooth  surfaces.  This  is  called  the  cleavage  and  the  planes 
the  cleavage  planes.  Study  galenite  and  note  how  it  cleaves  into  cubes; 
study  feldspar  or  calcite  and  see  how  these  cleave  into  rhombs.  Are  the 
angles  of  the  rhombs  constant  and  are  they  the  same  for  calcite  and  feld- 
spar? 

Some  minerals  break  in  characteristic  ways  other  than  along  cleavage 
planes.  Note  that  the  surfaces  of  broken  flint  are  curved  like  a  shell.  It  is 
said  to  have  a  conchoidal  fracture. 

Luster  is  the  appearance  of  the  mineral  when  seen  in  good  light  on  a 
freshly  exposed  surface.  Observe  the  vitreous  luster  of  obsidian,  the  pearly 
luster  of  selenite,  the  waxy  luster  of  chalcedony,  the  metallic  luster  of 
galenite. 

When  a  mineral  is  scratched  or  rubbed  on  a  piece  of  unglazed  porcelain 
so  as  to  leave  a  mark  it  shows  a  color  known  as  its  streak.  Thus  limonite  and 
hematite  are  frequently  very  similar  in  appearance  but  are  easily  dis- 
tinguished by  their  streak.  4.  Try  them  and  see  what  streak  each  gives. 

Then  within  narrow  limits  each  mineral  has  a  characteristic  hardness. 
This  is  so  valuable  a  distinguishing  character  that  a  scale  of  hardness  has 
been  fixed.  Thus  talc  has  a  hardness  of  i,  gypsum  2,  calcite  3,  fluorite  4^ 
apatite  5,  orthoclase  6,  quartz  7,  topaz  8,  corundum  9,  diamond  10.  5.  In 
so  far  as  you  have  these  in  your  collection  try  scratching  them  with  finger- 
nail, a  knife,  or  with  each  other  to  get  some  first-hand  knowledge  of  their 
relative  hardness.  Frequently  similar  appearing  minerals  are  distinguished 
by  their  hardness.  Thus  chalcopyrite  and  pyrite  at  times  look  much 
alike,  but  the  former  has  a  hardness  not  to  exceed  4,  while  the  latter  has 
at  least  a  hardness  of  6. 

Table  of  distinguishing  characters. — 6.  Fill  in  the  following  table  of 
the  minerals  listed  above,  arranging  them  now  not  alphabetically  but  in 
the  order  of  their  hardness.  Obtain  the  information  called  for  from  the 
minerals  themselves,  or  from  any  good  book  on  minerals  (see  Appendix) 
when  you  are  in  doubt.  Some  spaces  must  be  left  blank,  as  not  every 
mineral  will  have  the  characters  called  for. 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


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8    8 


COMMON  MINERALS  AND  ROCKS 


10  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Familiarize  yourself  with  the  minerals  in  your  collection  until  you  are 
reasonably  sure  that  you  can  identify  each.  7.  Then  try  to  name  the 
unnamed  specimens  that  will  be  furnished  you. 

Ores. — In  the  list  of  minerals  given"  above  are  several  ores  of  the  com- 
mon metals.  Galenite,  limonite,  hematite  and  pyrite,  malachite  and 
chalcopyrite,  sphalerite  and  cassiterite.  Your  table  will  show  the  chemical 
composition  of  each.  Galenite,  pyrite,  and  sphalerite  are  found  in  grains 
and  small  masses  in  the  limestone  of  this  region,  the  lead  and  zinc  blende 
in  paying  quantities  in  immediately  adjacent  territory.  8.  Look  up-  the 
method  of  reduction  of  some  one  of  these  ores  by  means  of  which  the  metal 
is  obtained  from  it  and  briefly  write  it  up  on  the  blank  page  opposite. 

Valuable  minerals. — Many  of  the  other  minerals  are  commercially 
valuable.  Corundum  because  of  its  hardness  is  the  essential  ingredient  of 
grinding- wheels.  Chalk  is  familiar  in  the  schoolroom.  Gypsum  yields 
plaster  of  Paris.  Kaolin  is  the  clay  from  which  our  fine  table  china  is  made. 
Mica  is  a  valuable  electrical  insulator  and  is  common  also  in  stove  doors. 
The  feldspars  and  the  clays  which  result  from  their  disintregration  yield 
aluminium.  Several  varieties  of  quartz  serve  as  valuable  gems,  such  as 
amethyst  and  rose  quartz,  while  the  clear  .crystals  are  the  "Hot  Springs 
diamonds." 

Rocks  are  classified  according  to  the  method  of  formation  into  sedi- 
mentary, igneous,  and  metamorphic.  9.  Briefly  state  the  method  of  forma- 
tion of  each  on  the  blank  page  that  follows. 

Sedimentary  rocks  are  laid  down  as  (i)  beds  of  more  or  less  waterworn 
fragments  of  shells,  corals,  or  other  calcareous  material,  (2)  beds  of  angular 
rock  fragments,  (3)  beds  of  gravel,  (4)  beds  of  sand,  or  (5)  beds  of  clay, 
(6)  beds  of  vegetable  material. 

What  is  sand?    gravel?     clay? 

These  beds  are  then  transformed  into  stone  by  pressure,  heat,  and  the 
action  of  various  cementing  substances,  working  separately  or  two  or  more 
in  unison.  The  calcareous  material  transforms  to  limestone,  or  dolomite 
if  magnesium  carbonate  predominates  rather  than  the  calcium  carbonate. 
The  angular  fragments  are  cemented  together  into  breccia,  the  gravel  into 
conglomerate,  sand  transforms  to  sandstone,  clay  into  shale,  and  vegetable 
material  into  peat  and  coal. 

Tests  for  rocks. — 10.  Study  your  specimens  of  limestone.  Is  it  easily 
scratched?  Put  a  drop  of  chlorhydric  acid  on  it  and  note  the  rapid 
discharge  of  carbon  dioxide,  a  gas  that  bubbles  up  through  the  drop  of  acid 
(effervescence).  Try  the  same  on  dolomite;  on  sandstone.  What  are  the 
results  on  these?  Examine  breccia,  conglomerate,  and  shale.  The  latter 
flakes  easily  and  emits  an  earthy  odor  when  you  breathe  upon  it. 


COMMON  MINERALS  AND  ROCKS  n 

Rocks  in  formation. — Visit  the  lake  shore  or  river  margin  where  deposits 
of  sand,  pebbles,  or  clay  are  being  made.  Dig  down  into  such  deposits  or 
study  the  face  of  railroad  cuts  or  other  excavations  to  see  how  .such  material 
is  laid  down.  n.  Make  a  drawing  on  the  opposite  page  to  show  this. 
Do  you  find  any  evidence  that  the  material  is  cementing  together  or  solid- 
ifying to  make  rock? 

The  stone  quarry. — 12.  Visit  a  stone  quarry  and  answer  the  following 
questions: 

Is  the  stone  in  layers? 

Are  the  layers  or  strata  horizontal  ? 

If  not,  what  is  the  angle  of  their  "dip"? 

1  What  is  the  "dip"  ? 


What  do  you  mean  by  the  "strike"  of  the  strata?. 


Are  the  layers  folded  at  all? 

What  are  bedding  planes  and  are  they  apparent? . 


Are  joints  apparent?  . . . 
Are  fossils  to  be  found? 
What  is  a  fossil?.. 


13.  Sketch  one  or  two  that  you  find. 

Geological  time. — Sedimentary  rocks  have  been  forming  through  many 
ages  and  contain  in  their  fossils  an  exceedingly  interesting  record  of  the 
changing  life  on  the  earth.  The  history  of  the  earth's  past  is  divided  into 
great  eras.  Just  as  human  history  is  divided  into  the  modern  era,  the 
medieval,  the  ancient,  an  earlier  era  of  dim  myth,  and  a  still  earlier  era  of 
which  we  know  nothing,  so  the  geological  history  of  the  earth  partially 
revealed  by  the  rock  record  is  divided  into  the  modern  or  Cenozoic  era, 
the  Mesozoic,  the  Paleozoic,  the  Proterozoic,  and  the  Archeozoic.  This 
entire  geological  time  spans  many  millions  of  years.  The  historian,  for 
convenience,  divides  the  great  eras  into  periods;  thus  the  ancient  era  is 
made  up  of  the  Babylonian  period,  the  Egyptian,  the  Grecian,  the  Roman. 
So  the  geologist  subdivides  the  great  geological  eras  into  periods  each 
characterized  by  its  own  peculiar  living  forms. 

Niagara  limestone. — The  bedrock  of  the  Chicago  region  is  the  Niagara 
limestone  formed  during  the  Paleozoic  era.  14.  Visit  the  Walker  Museum 
(or  similar  institution)  to  see  some  of  the  many  fossils  found  in  this  Niagara 
limestone  and  to  get  a  glimpse  also  of  the  many  animals  and  plants  that 
existed  in  the  Paleozoic  and  other  eras  of  the  earth's  geologic  past. 


12 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


Igneous  rocks  are  subdivided  into  volcanic  and  Plutonic  rocks. 
15.  Give  the  method  of  formation  and  the  distinguishing  characters  of 
each  on  the  opposite  blank  page.  It  will  be  evident  from  their  method  of 
formation  that  no  hard-and-fast  line  can  be  drawn  between  these  two 
sorts  of  igneous  rocks.  They  form  a  continuous  series  from  the  coarsely 
crystalline  Plutonic  rocks  to  the  glassy  and  more  or  less  porous  volcanic 
rocks.  Igneous  rocks  differ  greatly  also  in  chemical  composition.  If  the 
molten  material  from  which  the  rock  formed  contained  an  excess  of  silica 
and  only  bases  of  low  valence  like  potassium,  the  rock  is  acid  and  contains 
silicates  of  the  bases  together  with  much  free  quartz.  If  on  the  other  hand 
the  molten  material  contained  bases  of  high  valence  like  calcium  or  iron, 
the  resulting  rock  is  said  to  be  basic  and  contains  silicates  of  the  bases 
but  little  or  no  free  quartz.  Potassium  is  monovalent  and  can  take  up  in 
combination  relatively  little  silica  when  it  forms  its  silicate,  so  that  much 
free  silica  is  to  be  expected.  Iron,  however,  is  quadrivalent  and  can  take 
up  a  large  amount  of  silica  to  form  its  silicate,  so  little  free  quartz  is  found 
in  these  basic  rocks  (see  p.  62). 

Classification  of  igneous  rocks. — On  the  basis  of  these  two  things,  the 
texture  of  the  rocks  and  their  basidity,  the  classification  of  the  igneous 
rock  is  made.  In  the  table  below,  reading  from  left  to  right,  the  families 


GRANITE-RHYOLITE 
FAMILY 

SYENITE  -TRACHYTE 
FAMILY 

DlORITE-ANDESITE 

FAMILY 

GABBROBASALT 
FAMILY 

PERIDOTE 
FAMILY 

Quartz  and  orthoclase 
dominant 

Orthoclase  domi- 
nant. No  quartz 

Plagioclase 
dominant 

Labradorite  and 
pyroxene  dominant 

No  feldspar 
present 

Rhyolite  pumice 
Rhyolite  obsidian 

Granite 
Biotite-granite 

Trachyte 
Syenite 

Andesite 

Basalt-tuff 
Basalt 
Dolerite 

Horneblende- 
bearing  biotrte, 
granite,  etc. 

Diorite- 
porphyry 

Diabase 

Peridote 

Diorite 

Olivine- 
diabase 
Gabbro 

are  made  of  rocks  that  contain  less  and  less  free  quartz  and  whose  constit- 
uent minerals  are  increasingly  basic  silicates.  The  members  of  each  family, 
reading  down  in  the  series,  are  less  porous,  less  glassy,  the  crystals  of  the 
constituent  minerals  are  larger,  and  the  rocks  are  heavier,  since  elements, 
like  iron,  of  great  specific  gravity  are  replacing  lighter  ones,  like  potassium. 
What  is  a  porphyry?  an  amygdaloid? 


COMMON  MINERALS  AND  ROCKS  13 

Study  of  samples. — 16.  Study  now  the  igneous  rocks  in  your  collection 
with  the  explanation  in  mind  and  place  them  in  the  table.  Try  to 
make  out  the  constituent  minerals  and  to  recognize  them  by  the  characters 
already  studied.  Use  a  lens  to  assist  you  in  this  work.  Note  the  texture 
and  the  relative  weights  of  the  rock  specimens.  Verify  with  your  specimens 
the  following  additional  distinguishing  characters  that  will  help  in  the 
separation  of  these  rocks.  The  granites  contain  quartz  and  the  alkaline 
feldspars,  often  with  some  hornblende,  mica,  or  augite.  The  composition 
of  gneiss  is  the  same,  but  it  shows  evidence  of  stratification  (see  below). 
If  any  one  or  two  minerals  in  addition  to  the  essential  quartz  and  feldspar 
are.  especially  conspicuous  the  granite  is  named  accordingly  as  biotite- 
1  hornblende-granite. 

Syenite  contains  an  abundance  of  orthoclase,  usually  of  the  red  varieties, 
and  no  quartz.  Hornblende,  mica,  and  augite  may  one  or  all  be  present. 
It  is  a  Plutonic  rock  and  therefore  usually  coarse-grained.  The  correspond- 
ing volcanic  rock  is  trachyte,  finer  grained,  more  porous,  and  lighter  in  weight. 

In  the  diorites  the  dark  feldspars  predominate,  though  sometimes  the 
light-colored  plagioclases  are  abundant.  Quartz  is  present  and  also  often 
mica  and  hornblende,  but  not  in  predominating  quantities.  The  diorites 
are  Plutonic,  the  corresponding  volcanic  rocks  being  the  andesites. 

Gabbro  and  basalt  are  respectively  the  Plutonic  and  volcanic  members 
of  the  next  family.  They  are  dark,  heavy  rocks  with  labradorite  and 
augite  as  the  predominant  minerals.  The  gabbro  is  distinguished  from 
the  diabase  by  its  coarse  crystallization  and  by  the  large  quantity  of 
plagioclase  that  it  contains.  The  presence  of  chlorite  in  these  rocks  often 
gives  them  a  distinct  green  color  and  they  are  then  known  as  greenstones. 
The  peridote  contains  neither  quartz  nor  feldspar,  but  consists  of  such 
minerals  as  augite  and  amphibole. 

Metamorphic  rocks  were  originally  either  sedimentary  or  igneous,  but 
have  been  altered  greatly  by  heat,  pressure,  crumpling,  and  other  agencies, 
acting  singly  or  in  unison,  so  that  their  characteristics  have  been  materially 
changed.  Thus  limestone  and  dolomite  have  been  transformed  to  marbles 
(the  acid  test  still  distinguishes  them).  Sandstone  has  been  metamor- 
phosed to  quartzite,  which  is  recognized  by  its  hardness  and  conchoidal 
fracture.  The  shales  have  been  changed  to  slates  that  beak  into  thin  layers. 
The  granitic  rocks  have  been  altered  to  gneiss  or  schist,  the  former  showing 
evidence  of  layering  while  the  latter  is  flakey.  The  schists  are  named 
from  their  dominant  mineral:  micaceous  schist,  choritic  schist,  etc. 

Specimens  of  metamorphic  rocks. — Study  now  the  metamorphic  rocks 
in  the  collection  17.  Indicate  by  an  S,  I,  or  M  placed  beside  each  rock 
in  the  list  whether  it  is  sedimentary,  igneous,  or  metamorphic. 


14  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Glacial  drift. — -While  the  bedrock  of  the  Chicago  region  and  of  the 
adjacent  area  is  sedimentary,  the  glacial  drift — the  soil  and  rock  debris 
that  overlays  the  bedrock  for  the  most  part — contains  many  bowlders  and 
fragments  of  igneous  and  metamorphic  rocks  brought  to  our  region  from  the 
north  by  the  great  glaciers  that  invaded  this  territory  during  the  glacial 
epochs  in  relatively  recent  geological  time.  The  northern  part  of  Min- 
nesota, Wisconsin,  the  Upper  Peninsula  of  Michigan,  and  much  of  Canada 
are  occupied  by  these  igneous  and  metamorphic  rocks  of  the  Proterozoic  and 
Archeozoic  eras.  18.  Go  to  the  lake  shore,  the  gravel  pit,  or  the  piles  of 
bowlders  found  in  the  fields,  and  with  a  hammer  break  off  samples  of  these 
glacial  rocks  and  try  to  identify  them.  It  is  too  much  to  expect,  with  the 
brief  instructions  given  here  and  the  limited  facilities  at  the  hands  of  the 
student,  that  he  will  be  able  to  identify  all  these  with  certainty.  Some  of 
them  with  clear  characters  and  readily  recognized  mineral  ingredients  will 
be  easily  identified.  Still  the  attempt  will  help  him  to  gain  some  facility 
in  recognizing  the  component  minerals  and  in  judging  relative  weights  and 
textures.  Possibly,  too,  it  may  serve  as  an  incentive  to  more  thorough 
courses  in  this  fascinating  study  of  minerals  and  rocks.  19.  Name  and 
label  such  as  you  can  identify  with  reasonable  certainty  and  make  a  list  of 
these  on  the  opposite  page,  at  the  same  time  classifying  them  as  sedimen- 
tary, igneous,  and  metamorphic. 

Rocks  of  commercial  value. — Some  of  the  rocks  listed  are  of  large 
commercial  value.  Much  of  the  copper  in  the  famous  mines  of  northern 
Michigan  occurs  as  amygdaloidal  grains  or  as  a  cement  in  a  conglomerate 
rock.  Granite  and  syenite  are  familiar  as  building  stones.  Limestone, 
marble,  and  sandstone  serve  a  similar  purpose.  Slate  is  a  common  roofing 
material,  replaced  now  largely  by  tile  or  asbestos  (fibrous  serpentine) 
shingles.  One  variety  of  serpentine,  verd  antique,  is  used  as  an  ornamental 
stone.  Limestone  is  heated  and  transformed  to  CaO,  the  CO2  being  driven 
off  by  the  heat.  This  is  the  "unslacked  lime"  used  in  making  plaster. 


THE  STARS  AND  OUR  SOLAR  SYSTEM 

The  polar  constellations. — 

The  Big  Bear. — See  in  the  northern  sky  the  Big  Dipper.  The  two 
stars  forming  the  side  of  the  Dipper's  bowl  farthest  from  the  handle  are 
commonly  called  the  pointers,  for  if  a  line  be  drawn  through  them  and 
extended  northward  it  leads  to  Polaris,  the  polestar.  Find  this  in  the  sky 
and  20  draw  on  the  opposite  page  the  Big  Dipper  as  it  is  seen  now  when 


FIG.  i. — Principal  stars  of  Ursae  Major.  The  long  tail  is  a  late  addition  to  the  old 
mythological  figure.  Dots  are  fifth-magnitude  stars,  crosses  fourth-magnitude,  etc. 

you  are  facing  north  about  9:00  P.M.  Draw  the  polestar  also  on  the 
same  diagram,  showing  its  relation  to  the  Big  Dipper  both  in  direction  and 
distance. 

The  middle  star  of  the  Dipper  handle  is  a  doublet,  both  members  being 
visible  to  the  naked  eye.  Can  you  see  them  both?  They  are  named 
Mizar  and  Alcar,  the  Horse  and  Rider,  the  latter  being  identified  in  Greek 
legend  with  the  lost  Pleiad  (see  p.  19).  The  polestar  is  at  the  end  of  the 

15 


1 6  GUIDE  IN  PHYSICAL  NATURE-STUDY 

handle  of  the  Little  Dipper,  most  of  the  stars  of  which  are  dim.  With  the 
aid  of  the  diagram  (Fig.  i)  identify  the  stars  of  the  constellation  of  the 
Big  Bear,  Ursa  Major. 

Polaris. — 21.  Cut  a  piece  8  inches  square  from  a  f-inch  board  to 
serve  as  a  baseboard.  At  the  midpoint  of  the  opposite  sides  fasten  two 
i -inch- wide  1 2-inch  uprights  of  light  stuff.  Cut  a  square  strip  of  the 
f -inch  stuff  8  inches  long  and  tack  to  this,  at  the  midpoint  of  each,  a  1 2- 
inch  strip  of  light  stuff  an  inch  wide  so  that  they  will  lie  at  right  angles  to 
each  other.  Run  brads  through  corresponding  points  near  the  upper  ends 
of  the  uprights  and  into  the  centers  of  the  opposite  ends  of  the  f-inch 
square  strip.  Cut  an  8-inch  semicircle  out  of  cardboard  and  fasten  to  the 
i2-inch  strip  so  that  the  diameter  of  the  semicircle  will  run  through  the 
axis  line  on  which  the  f-inch  strip  rotates.  Fasten  on  one  of  the  uprights 
a  Wire  pointer  so  that  when  the  12 -inch  strip  is  level  (after  leveling  the  base- 
board, see  below)  its  point  will  stand  at  the  midpoint  of  the  semicircle. 
Mark  this  point  O. 

Float  the  baseboard  on  a  bucketful  of  water  that  has  been  set  out  of 
doors  on  some  support,  like  a  soap  box.  This  will  insure  that  the  base- 
board is  perfectly  level.  The  same  result  may  be  achieved  by  laying  a 
cheap  level  first  on  one,  then  on  the  other  of  the  two  adjacent  edges  of  the 
baseboard  and  blocking  up  the  corners  when  set  on  the  box  until  level. 
With  the  axis  of  the  apparatus  turned  east  and  west  set  the  1 2-inch  strip 
so  that  it  points  to  the  polestar;  sight  along  the  strip  to  make  sure  that  it 
is  pointed  exactly.  Mark  the  point  on  the  semicircle  which  the  pointer 
now  indicates.  Measure  the  area  between  this  point  and  O  in  degrees. 
(Use  a  protractor — a  small  semicircle  divided  into  degrees  and  fractions 
of  a  degree.)  How  does  the  angle  between  the  two  points  agree  with  the 
latitude  of  the  place  where  you  live  as  you  find  it  from  the  map?  Why 
this  relation? 

Constellation  of  Bootes. — Extend  the  curved  line  of  the  Big  Dipper 
handle  in  a  direction  away  from  the  bowl,  and  about  the  length  of  the 
Dipper  from  the  end  of  its  handle  is  a  first-magnitude  star,  Arcturus,  in  the 
constellation  of  Bootes,  the  Hunter.  The  other  stars  of  Bootes  (Fig.  2) 
are  shown  in  relation  to  Arcturus.  The  two  northernmost  are  near  the 
star  at  the  end  of  the  Dipper  handle.  22.  On  the  opposite  page  give  the 
legends  of  Ursa  Major  and  Ursa  Minor  and  Bootes,  the  Hunter. 

Cassiopeia. — On  the  opposite  side  of  the  pole  from  the  Dipper  and  about 
as  far  from  Polaris  is  Cassiopeia's  Chair,  an  open  W  of  rather  bright  stars 
which  with  the  addition  of  one  rather  dim  one  becomes  a  chair.  Find  this 
constellation  and  23  diagram  it  on  the  opposite  page,  showing  its  relation 
to  Polaris,  in  a  way  similar  to  the  diagram  of  Bootes,  Figure  2. 


THE  STARS  AND  OUR  SOLAR  SYSTEM  17 

Cephas. — A  line  drawn  through  the  stars  at  the  tips  of  the  chair  legs 
in  an  anti-clockwise  direction  reaches  a  star  of  the  third  magnitude  in  the 
constellation  Cephas,  half  again  as  far  from  Cassiopeia  as  the  full  length  of 
the  W.  Between  this  and  the  polestar  and  directly  in  line  with  the  two 


FIG.  2. — Bootes  and  the  Hunting  Dogs,  showing  the  principal  Stars 

is  another  third-magnitude  star,  also  in  Cephas.  These  two  serve  as  pole- 
star  pointers  quite  as  well  as  the  two  in  the  Dipper.  The  other  stars  of 
Cephas  are  arranged  somewhat  as  in  Figure  3.  Identify  the  constellation 
in  the  sky. 

Perseus. — The  star  at  the  base  of  the  back  of  Cassiopeia's  Chair  and 
the  one  in  the  angle  of  the  back  may  be  used  as  pointers  to  find  the  con- 
stellation Perseus.  The  line  through  these,  extended  in  the  opposite  direc- 
tion from  Cephas  about  as  far  from  Cassiopeia  as  are  the  polar  pointers 
of  Cephas,  reaches  the  brightest  star  of  Perseus  (a  Perseus).  Run  a 


i8 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


line  from  the  pole  through  this  star  and  extend  it  about  as  far  as  the  two 
stars  at  the  bottom  of  the  Dipper  are  from  each  other  and  it  reaches  Algol, 
the  demon  star,  a  variable,  also  a  bright  star  of  Perseus.  24.  Draw  on 
the  opposite  page  the  principal  stars  of  Perseus  as  you  find  them  on  a  star 
map  and  identify  them  in  the  sky  at  the  place  indicated. 

Andromeda.— From  the  polestar  draw  a  line  through  the  end  of  the  W 

farthest  from  the  back  of  the 
chair  in  Cassiopeia  and  extend 
it  about  as  far  from  Cassiopeia 
as  the  latter  is  from  the  pole 
and  it  reaches  a  bright  star,  one 
of  the  four  that  form  a  great 
quadrilateral  known  as  "the 
square  of  Pegasus."  The  one 
first  noted  is  really  in  Androm- 
eda, the  other  three  in 
Pegasus.  A  diagonal  of  "the 
square"  drawn  through  the  star 
of  Andromeda  and  extended 
toward  Perseus  about  the 
diameter  of  the  square  en- 
counters another  bright  star 
of  Andromeda.  25.  Copy  on 
the  opposite  page,  from  a  star 
map,  the  principal  stars  of 
Andromeda  and  try  to  identify 


them  in  the  sky,  now  that  you 
know  where  to  look  for  them. 
Include  them  in  an  outline 
figure  of  Andromeda  similar  to 
that  of  Bootes  in  Figure  2. 


FIG.  3. — The  figure  of  Cephas  and  the  prin- 
cipal stars  of  the  constellation.  The  king  stands 
on  the  North  Pole. 


The  Dragon. — Draw  a  line  from  the  star  at  the  base  of  the  chair  back 
through  the  northernmost  one  of  the  pair  of  polar  pointers  in  Cephas  and 
extend  it  about  as  far  toward  Cephas  as  Cassiopeia  is  distant  from  him  to 
a  bright  star  in  the  head  of  the  Dragon  (a  Draco  or  Theban) .  This  Dragon's 
Head  is  made  of  four  stars,  two  of  which,  the  eyes,  are  quite  bright.  The 
body  of  the  dragon  runs  back  toward  Cephas,  then  turns  in  the  opposite 
direction  to  partly  encircle  the  Little  Dipper.  Its  tail  lies  between  the 
Big  and  Little  Dippers.  26.  Draw  a  diagram  of  Draco. 

The  Swan. — Draw  a  line  from  the  star  in  the  angle  of  the  back  of  the 
chair  through  the  one  at  the  base  of  the  back  and  extend  it  in  the  opposite 


THE  STARS  AND  OUR  SOLAR  SYSTEM  19 

direction  from  Perseus  about  twice  as  far  as  the  latter  is  from  Cassiopeia 
and  a  first-magnitude  star  is  reached,  Deneb,  in  the  constellation  Cygnus, 
the  Swan.  27.  Copy,  on  the  first  blank  page  following,  the  figure  of  the 
Swan  from  some  star  map  showing  the  constellation,  indicate  the  principal 
stars,  and  also  show  why  this  constellation  is  sometimes  known  as  the 
Northern  Cross.  28.  On  the  same  page  give  briefly  the  legend  of  Cygnus. 

Other  first-magnitude  stars. — Imagine  a  line  drawn  from  the  polestar 
to  Deneb.  Through  Deneb  at  right  angles  to  this  line  draw  a  line  on  the 
side  opposite  that  which  faces  the  square  of  Pegasus,  to  a  first-magnitude 
star  about  half  as  far  from  Deneb  as  the  latter  is  from  the  pole.  This 
star  is  Vega  in  the  constellation  of  the  Lyre. 

"On  the  opposite  side  of  the  polestar  from  Vega  and  nearly  as  far  from 
it  lies  Capella,  a  first-magnitude  star  of  the  constellation  Auriga  the  Char- 
ioteer. Why  was  Auriga  given  a  place  among  the  immortals? 

How  many  first-magnitude  stars  lie  within  50°  of  the  North  Pole  and 
what  are  they?  29.  Make  a  list  of  them  here  and  of  the  constellations 
in  which  they  are  found. 

The  zodiacal  constellations  in  December  evenings  (or  early  mornings 
of  September). — 

Taurus. — The  Pleiades  is  a  group  of  six  naked-eye  stars  close  together 
in  the  form  of  a  very  little  dipper  on  the  meridian  about  9:30  toward  the 
close  of  December.  Find  it  in  the  sky.  Very  good  eyes  make  out  seven 
stars;  the  "lost  one"  is  identified  now  as  Alcar  of  the  Dipper  (see  the  Source 
Book  of  Physical  Nature-Study}. 

To  the  east  of  the  Pleiades  notice  a  V-shaped  group,  the  Hyades,  one 
star  of  which,  Aldebaran,  is  of  the  first  magnitude.  Both  the  Pleiades  and 
Hyades  are  in  the  constellation  of  Taurus,  the  Bull.  30.  On  the  following 
blank  page  sketch  the  outline  of  Taurus  and  show  the  principal  stars, 
copying  the  figure  from  some  star  map  or  other  source. 

Orion. — Run  a  line  from  the  Pleiades  through  Aldebaran  and  farther 
to  the  east  to  a  line  of  three  bright  stars,  the  belt  of  Orion.  To  the  north 
of  this  is  a  bright  reddish  star,  Betelgeuse,  and  to  the  south  another  first- 
magnitude  star  of  bluish  cast,  Rigel.  The  constellation  of  Orion  is  the  most 
brilliant  one  in  the  sky.  31.  On  the  blank  page  that  follows  copy  the 
outline  of  Orion  from  some  star  map  and  show  also  the  principal  stars. 
Identify  as  many  as  possible  in  the  sky.  If  possible  see  the  middle  star 
of  the  dagger  handle  hanging  from  Orion's  belt  through  a  telescope.  It  is 
imbedded  in  the  famous  nebula  of  Orion. 

Canis  Major  and  Canis  Minor. — The  most  brilliant  single  star  in  the 
heavens  is  Sirius.  It  lies  to  the  east  of  (below)  Orion  in  the  constellation 
of  the  Great  Dog,  Canis  Major.  Make  Betelgeuse  and  Sirius  the  basal 


20 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


corners  of  an  equilateral  triangle,  the  apex  a  bright  star  to  the  north,  and 
so  locate  Procyon  in  the  constellation  of  the  Lesser  Dog,  Canis  Minor. 
The  two  dogs  are  supposed  to  be  following  the  hunter  Orion,  who  stands 
with  club  uplifted  facing  the  bull.  32.  On  one  of  the  blank  pages  following 
briefly  give  the  legend  connected  with  these  constellations. 

The  Twins. — Make  Aldebaran  and  Sirius  the  basal  corners  of  a  larger 
equilateral  triangle  with  the  apex  to  the  north  and  so  locate  one  of  a  pair 
of  bright  stars,  Pollux  of  Castor  and  Pollux,  the  twins,  in  the  constellation 
of  Gemini.  33.  Diagram  the  stars  of  Gemini  and  identify  as  much  of 
the  constellation  as  possible  in  the  sky. 

Taurus  and  Gemini  are  both  among  the  zodiacal  constellations.  What 
is  the  zodiac? 


34.  Fill  in  the  following  tabulation: 


NAME  OF  THE  ZODIACAL  CONSTELLATIONS 

SIGN  OF  THE 
CONSTELLATION 

I  

2  

7 

4  

z.  . 

6  

7  

8  

9  

10  

ii  

12  

THE  STARS  AND  OUR  SOLAR  SYSTEM  21 

From  Aldebaran  through  the  Pleiades  draw  a  line  and  extend  it  beyond 
the  Pleiades  half  again  as  far  as  Aldebaran  is  from  the  Pleiades  to  a  fairly 
bright  star,  Alpha,  of  the  constellation  Aries  the  Ram.  Near  this  star  directly 
toward  the  pole  is  a  group  of  three  stars,  the  Triangle,  which  will  help  to 
locate  Aries.  This  is  the  first  of  the  zodiacal  constellation.  The  last,  the 
constellation  of  the  Fishes,  is  also  now  visible,  though  the  stars  that  make 
it  are  dim.  It  is  an  irregular  line  of  stars  that  starts  south  of  Andromeda 
about  halfway  between  Alpha  Aries  and  the  square  of  Pegasus,  runs  to  a 
point  due  south  of  Aries,  about  as  far  from  the  pole  as  is  the  belt  of 
Orion,  and  thence  down  toward  the  horizon  to  the  west  of  the  square 
of.  Pegasus. 

Southern  constellations  in  December  (or  early  mornings  of  late  July). — • 
Early  in  the  evenings  of  December  (6:00  P.M.),  when  the  square  of  Pegasus 
is  about  on  the  meridian,  a  line  drawn  from  the  pole,  past  the  westernmost 
star  of  the  square  and  continued  to  the  southern  horizon,  reaches  a  first- 
magnitude  star,  Formalhaut,  in  the  constellation  of  the  Southern  Fish.  The 
other  stars  of  this  constellation  are  just  visible.  On  the  line  from  Formal- 
haut to  Deneb  and  about  halfway  between  the  two  is  a  line  of  three  third- 
magnitude  stars  that  mark  Aquarius,  the  Water  Bearer.  This  constellation 
is  pretty  well  spread  out  but  may  be  identified  by  the  aid  of  the  plani- 
sphere (p.  23),  which  should  be  put  together  now  to  help  locate  the 
constellations  that  follow. 

To  the  east  of  the  meridian,  also  low  down  in  the  south,  is  a  nearly  hori- 
zontal group  of  three  pairs  of  moderately  bright  (one  second-magnitude,  five 
third-magnitude)  stars  in  the  constellation  of  Cetus,  the  Whale.  Five  other 
stars  grouped  together  farther  to  the  east  also  lie  in  the  constellation. 
Note  that  in  this  region  of  the  sky  where  Aquarius  lies  there  are  also  to 
be  found  the  fishes  of  the  zodiacal  constellations,  the  Southern  Fish,  the 
Whale.  What  is  the  legend  connected  with  these  several  constellations  ? 
35.  Outline  it  briefly  on  the  opposite  page.  The  series  of  constellations 
connected  with  this  legend  continues  to  pass  in  review  evenings  through 
the  spring  and  early  summer. 

Eridanus. — In  January,  when  the  Pleiades  is  on  the  meridian,  there  is 
a  widespreading  constellation  zigzagging  back  and  forth  across  the  meridian 
in  the  south  near  the  horizon,  the  great  river  Eridanus.  Trace  it  westward 
from  Rigel  nearly  to  the  Whale,  then  east  again  past  the  meridian  west  of 
south  to  the  horizon.  36.  Copy  the  constellation  from  some  star  map,  on 
the  blank  page  opposite. 

More  zodiacal  constellations  visible  in  March  evenings  (or  early  morn- 
ings of  October). — When  Castor  and  Pollux  are  on  the  meridian  in  the 
evenings  of  the  middle  of  March  locate  a  group  of  stars  shaped  like  a 


22  GUIDE  IN  PHYSICAL  NATURE-STUDY 

reversed  2,  to  the  east  of  them  and  about  a  third  of  the  way  to  the  horizon. 
At  what  time  could  you  see  it  now  ?  Regulus,  a  brilliant  first-magnitude 
star,  is  at  the  end  of  the  base  of  the  figure.  Regulus,  Procyon,  Betelgeuse, 
and  Pollux  make  a  diamond-shaped  figure,  while  Regulus,  the  star  in  the 
bottom  of  the  Dipper  farthest  from  the  handle,  and  Denebola,  another 
bright  star,  make  an  isosceles  triangle.  Denebola  is  in  line  with  the  pole- 
star  and  the  star  in  the  bottom  of  the  Dipper  nearest  the  handle  and  about 
as  far  from  this  star  as  it  is  from  the  pole.  Denebola  and  Regulus  are  both 
in  the  constellation  of  Leo,  the  Lion.  37.  Sketch  the  figure  of  the  Lion 
and  show  the  chief  stars. 

Southern  sky  in  March. — The  whole  southern  sky,  close  to  the  horizon, 
is  now  occupied  by  the  constellation  of  the  Ship  or  Ark.  All  the  stars 
from  east  to  west  south  of  the  Great  Dog  are  in  this  constellation.  Identify 
it  with  the  aid  of  the  planisphere.  38.  Sketch  the  Ship  or  Ark,  copying 
the  figure  from  some  star  map  and  show  the  principal  stars. 

Zodiacal  constellations  in  April  (or  early  mornings  in  November): — 
About  8 : 30  P.M.  in  the  latter  part  of  April,  when  the  pointers  of  the  Dipper 
are  on  the  meridian,  draw  a  line  from  the  lip  of  the  Dipper  through  the 
star  in  its  bottom  near  the  handle  and  extend  it  across  the  sky  to  a  first- 
magnitude  star,  Spica,  in  the  constellation  Virgo,  the  Virgin.  Spica  and 
Arcturus  are  at  the  basal  corners  of  an  isosceles  triangle  with  Denebola  at 
the  apex.  39.  Copy  here  the  chief  stars  of  this  constellation.  Try  to 
identify  them  in  the  sky.  When  can  you  see  Spica  now  ? 

Southern  constellations  in  April. — South  of  Spica  and  a  little  west 
also,  in  a  line  from  the  pole  through  the  star  in  the  top  of  the  Dipper's 
bowl  near  the  handle  and  extended  nearly  to  the  southeastern  horizon, 
is  a  semicircular  group  of  quite  bright  stars,  Corvus,  the  Crow.  40.  Draw 
the  group  on  the  next  blank  page.  From  east  of  Corvus  running  west 
across  the  southern  sky  see  a  line  of  stars,  mostly  faint,  that  leads  nearly 
over  to  Procyon,  the  sea  monster,  Hydra. 

The  zodiac  in  May. — Late  in  the  evening  in  the  latter  part  of  May, 
when  Arcturus  is  on  the  meridian,  draw  a  line  through  the  pointer  of  the 
Dipper  farthest  from  the  polestar  and  the  star  at  the  end  of  the  Dipper's 
handle.  Continue  it  across  the  sky  to  the  southeastern  horizon  to  a  bright 
star,  An  tares,  in  the  constellation  of  the  Scorpion.  41.  Sketch  the  other 
stars  of  this  constellation  on  the  blank  page  opposite  and  identify  them  in 
the  sky.  This  is  easy  because  of  their  arrangement  in  triplets. 

A  southern  constellation. — On  either  side  of  the  meridian  close  to  the 
southern  horizon  are  two  second-magnitude  stars  that  locate  the  Centaur 
or  Noah  of  the  earlier  legends.  All  the  stars  that  stretch  along  the  southern 
sky  west  of  these  two  are  in  this  constellation. 


THE  STARS  AND  OUR  SOLAR  SYSTEM  23 

A  planisphere. — 42.  It  is  quite  a  feasible  undertaking  for  grade  pupils 
to  construct  a  planisphere  which  will  enable  them  to  determine  which  stars 
are  visible  at  any  time  of  the  night  throughout  the  year  and  to  see  their 
relative  positions.  It  is  well  for  the  teacher  to  construct  one  so  that  she 
may  be  competent  to  give  directions.  Proceed  as  follows:  Cut  a  card, 
board  circle  of  3!  inches  in  radius.  With  pencil  compass  draw  light  con- 
centric circles  every  J  inch.  The  outer  J  inch  will  serve  as  a  border  for 
the  names  of  the  month  to  be  filled  in  later.  These  concentric  lines  will 
be  10°  apart  and  will  extend  down  40°  below  the  equator,  which  will 
include  all  stars  we  see  in  our  latitude.  Draw  ink  circles  to  represent 
Arctic  Circle,  Tropic  of  Cancer,  Equator,  Tropic  of  Capricorn.  With  the 
compass  set  at  3^  inches  start  at  any  point  on  the  circle  of  that  radius 
and  mark  six  points  on  the  circle,  each  distant  from  the  adjacent  ones  by 
this  amount.  From  the  center  draw  light  ink  lines  through  these  points, 
thus  dividing  the  circles,  except  the  outermost,  into  six  sectors.  Bisect 
these  sectors,  making  twelve  divisions  of  each  circle.  Fill  in  the  con- 
stellations, showing  only  the  principal  stars,  copying  them  from  star  maps 
such  as  those  given  in  the  Source  Book  of  Physical  Nature-Study  or  from 
some  published  planisphere.  The  o°  line  radiating  from  the  pole  is  the 
one  that  just  touches  the  tip  of  the  front  leg  of  Cassiopeia's  Chair.  The 
30°  line  goes  through  Aries.  Continue  labeling  each  radiating  line  60°,  90°, 
etc.  The  o°  line  falls  at  March  22,  the  90°  line  at  June  21,  the  180°  line 
at  September  20,  and  the  270°  line  at  December  21.  Subdivide  the  s'pace 
between  the  two  outer  circles  into  twelve  equal  lengths  so  that  the  dates 
given  in  these  months  will  fall  at  the  points  indicated  and  put  the  name  of 
a  month  in  each  space. 

Cut  two  other  cardboard  circles  of  3^  inches  in  radius.  In  one  cut 
a  hole,  marking  the  outline  for  it  as  follows:  Draw  a  radius  of  this  circle 
on  the  cardboard:  2§  inches  from  the  circumference  of  the  circle,  mark  a 
point  on  this  radius,  and  draw  a  cross-line  at  right  angles  to  the  radius  at 
this  point.  On  the  radius  extended  to  make  it  a  diameter  mark  points 
J  and  4^  inches  from  the  point  where  the  radius  meets  the  circumference 
of  the  circle.  The  portion  of  the  radius  between  these  will  be  the  minor 
axis  of  an  ellipse  that  is  to  be  cut  out.  On  the  line  drawn  at  right  angles 
to  the  radius  mark  points  2\  inches  on  each  side  of  the  radius.  The  line 
5  inches  long  between  these  will  be  the  major  axis.  Stick  two  pins  into 
the  major  axis,  one  on  each  side  of  the  minor  axis  and  i^  inches  from  it 
Tie  a  loop  of  string  of  such  length  that  when  it  is  slipped  over  the  two 
pins  and  extended  by  a  pencil  point  the  latter  will  just  reach  an  end  of  the 
minor  axis.  Move  the  pencil  about  the  pins  as  if  trying  to  draw  a  circle. 
An  ellipse  is  drawn  that  is  J  inch  distant  at  its  nearest  approach  from  the 


24  GUIDE  IN  PHYSICAL  NATURE-STUDY 

circumference  of  the  circle.  With  a  sharp  penknife  cut  this  out  from  the 
circular  card. 

Stick  a  pin  through  the  center  of  the  circular  star  map,  the  head  on 
the  side  showing  the  stars.  Stick  it  also  through  the  center  of  the  whole 
cardboard  circle.  Bend  it  close  to  the  head  so  that  the  star  map  will  revolve 
about  the  pin,  the  other  card  serving  as  the  back.  Paste  a  piece  of  paper 
over  the  pointed  end  of  the  pin  to  hold  it  in  place. 

Lay  the  circle  in  which  the  elliptical  hole  has  been  cut  on  the  star 
map -so  that  its  edge  will  coincide  with  the  outermost  circle  drawn  on  the 
star  map.  The  names  of  the  months  should  show  beyond  it.  Paste  four 
narrow  strips  of  paper  at  90°  intervals  from  the  edge  of  the  upper  circle 
to  the  edge  of  the  lower,  folding  them  snugly  around  the  edge  of  the  star 
map  so  that  it  will  move  freely.  Mark  the  point  where  the  radius  crosses 
the  narrow  strip  of  card  12  noon,  the  opposite  edge  of  this  upper  circle 
12  midnight.  With  the  latter  point  near  you  and  the  former  away  from 
you,  mark  the  midpoint  of  the  left-hand  semicircle  6:00  P.M.,  of  the  right- 
hand  semicircle  6:00  A.M.  The  interval  between  noon  and  6:00  P.M.  may 
be  divided  into  six  equal  portions  and  marked  with  the  hours  and  so  on 
for  each  other  quarter  of  the  circle. 

If  the  star  map  be  rotated  between  the  two  smaller  cardboard  circles, 
the  area  that  shows  in  the  ellipse  is  the  portion  of  the  sky  that  is  visible. 
If  it  is  turned  so  that  mid-December  coincides  with  6:00  P.M.,  the  elliptical 
opening  will  show  what  constellations  are  then  visible.  Stand  out  of 
doors  facing  north.  Hold  the  planisphere  overhead,  face  down,  the  North 
Pole  turned  north,  noon  to  the  south.  The  morning  side  now  shows  the 
eastern  horizon,  the  evening  the  western. 

A  small  model  of  the  planisphere  as  described  is  figured  here  and 
may  be  put  together  as  follows:  43.  Remove  the  sheets  on  which 
Figures  4  and  5  are  printed.  Paste  both  sheets  to  thin  cards  and  cut 
them  out.  Cut  out  another  circular  card  the  same  size  as  Figure  5,  with- 
out the  four  flaps,  but  do  not  cut  out  the  elliptical  hole.  Run  a  pin 
through  the  center  of  Figure  4,  then  through  the  center  of  the  addi- 
tional circular  card.  Finish  the  planisphere  as  directed  above,  using  the 
strips  projecting  from  the  margin  of  Figure  5  to  fold  around  the  edge  of 
Figure  4  and  paste  to  the  circular  back. 

Planets. — Consult  the  almanac  and  find  in  what  constellations  Mars, 
Jupiter,  and  Saturn  are  now  in,  and  through  what  constellations  they  will 
move  the  remainder  of  this  year.  44.  Record  the  findings  on  the  opposite 
-blank  page. 

Find  and  45  record  also  the  morning  and  evening  stars  for  the 
year. 


THE  STARS  AND  OUR  SOLAR  SYSTEM 


FIG.  4.— The  star  map  for  the  planisphere 


26 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


FIG.  5. — Diagram  of  the  front  of  the  planisphere 

To  put  the  planisphere  together  paste  Fig.  4  smoothly  on  a  thin  card  and  cut'it  out. 
Do  the  same  for  Fig.  5,  but  after  it  is  pasted  on  the  card,  with  a  sharp  penknife,  cut 
out  the  ellipse  from  the  card.  Cut  a  second  card  circle  the  size  of  the  circle  of  Fig.  5 
and  mark  its  center.  Run  a  pin  through  the  center  of  Fig.  4  and  through  the  center  of 
this  circular  card  placed  below  Fig.  4.  Lay  Fig.  5  on  Fig.  45  its  circular  edge  just  inside 
the  strip  bearing  the  names  of  the  months.  Bend  the  four  flaps  on  Fig.  5  over  the  edge 
of  Fig.  4  and  paste  them  to  the  circular  card  below.  Bend  the  pin  so  that  its  end  will 
lie  down  against  the  circular  card  back  and  hold  it  in  place  by  a  piece  of  paper  pasted 
over  it. 


THE  STARS  AND  OUR  SOLAR  SYSTEM  27 

Changes  in  the  moon. — Keep  record  for  a  month  of  the  change  in  the 
moon.  46.  Make  a  calendar  for  a  month  by  ruling  the  opposite  page  so 
as  to  give  an  inch  square  for  each  day.  In  each  square  draw  a  figure  to  show 
the  shape  of  the  moon  for  that  date  in  so  far  as  it  is  visible;  or  on  a  still 
larger  sheet  of  paper,  similarly  ruled,  paste  figures  cut  from  paper  to  show 
the  shape  of  the  moon. 

When  the  moon  is  new,  how  long  after  sundown  does  it  set? 

When  it  is  at  first  quarter? 

When  it  is  full,  how  long  after  sunset  does  it  rise? 

When  it  is  at  third  quarter? 

47.  Draw  a  diagram  to  show  the  relations  of  the  shape  of  the  moon 
to  the  relative  positions  of  sun  and  moon.  Why  do  we  not  have  an  eclipse 
of  the  sun  every  time  the  moon  is  new? 

The  sun. — 48.  Fasten  a  coarse  wire  horizontally  across  a  south  window- 
pane.  Lay  a  good-sized  piece  of  brown  paper  down  on  the  floor  so  that 
the  shadow  of  the  wire  about  crosses  its  middle.  Draw  pencil  lines  on  the 
floor  at  the  corners  of  the  paper  when  it  is  spread  out  so  that  it  may  be 
laid  down  repeatedly  in  the  same  position.  Draw  a  pencil  line  on  the 
paper  to  coincide  with  the  shadow  of  the  wire  and  date  it.  Every  few 
days  through  the  school  year  repeat  this  observation.  What  do  the  series 
of  records  show?  Can  you  explain  the  results? 

49.  Smoke  a  piece  of  glass  by  holding  it  over  a  candle  flame  until 
it  is  covered  with  a  thin  layer  of  soot.  Through  this  look  at  the  sun 
and  see  if  you  can  see  any  sun  spots.  Draw  a  2-inch  circle  to  represent 
the  sun  and  indicated  the  position  of  the  sun  spot  on  it.  Date  it  and 
record  the  time  of  your  observation.  Repeat  the  observation  on  several 
successive  days  and  see  if  the  spot  changes  its  position.  You  may  be  able 
to  watch  a  spot  cross  the  disk  of  the  sun.  If  so,  twice  the  time  required 
for  such  a  passage  is  equal  to  what?  Confirm  your  results  from  the  time 
given  in  the  astronomies. 


SOME  TOYS  THAT  WORK  BY  AIR 

To  make  the  paper  windmill. — 50.  Take  a  6-inch  square  of  paper, 
preferably  colored  paper.  If  the  paper  is  not  already  cut  in  such  form, 
proceed  as  follows  to  cut  a  6-inch  square  out  of  any  rectangular  sheet  of 
larger  size.  From  any  corner  of  the  sheet  measure  6  inches  along  each 
adjacent  side,  and  mark  the  points.  Fold  the  corner  over  and  crease  the 
paper  along  the  line  connecting  the  marked  points.  With  the  scissors, 
cut  the  paper  close  to  the  folded-over  edges. 

Draw  lines  on  the  6-inch  square,  running  from  each  of  two  adjacent 
corners  to  the  diagonally  opposite  corners.  Cut  in  from  the  corners  along 
these  lines  to  within  a  half-inch  of  the  intersecting  lines.  Lay  the  left 
hand,  back  down,  on  the  paper,  the  fingers  about  at  the  center.  With 
the  right  hand  fold  in  any  one  corner  and  hold  it  with  thumb  and  finger 
of  the  left  hand.  In  the  same  way  fold  in  every  alternate  corner  around  the 
square,  and  when  all  are  in  hand  run  a  pin  through  the  four  infolded  corners 
and  also  through  the  center  of  the  square.  Thrust  this  pin  into  a  wood 
handle  and  the  windmill  is  complete. 

51.  An  eight-point  windmill  may  be  made  in  place  of  the  four-point,  as 
follows:  It  makes  the  mill  more  attractive  if  paper  of  two  colors  is  used. 
Cut  a  6-inch  square  of  paper  of  each  color,  and  cut  in  from  the  corners  as 
before.  On  one  paper  make  a  half-inch  cut  at  the  inner  end  of  each  diagonal 
cut  on  the  left-hand  blades,  making  it  at  right  angles  to  the  edge.  Lay 
this  square  upon  the  table,  the  second  square  upon  it  so  that  the  centers 
coincide  and  so  that  the  corners  of  the  upper  sheet  are  midway  between 
the  corners  of  the  lower  sheet.  Then  insert  each  alternate  edge  of  the 
upper  blades  into  the  cuts  on  the  lower  blades.  Then  fold  over  all  the  inner 
points  as  before  and  run  the  pin  through  them  and  through  the  centers 
of  the  two  sheets.  Stick  the  pin  into  a  handle. 

To  make  the  wooden  windmill. — 52.  Cut  two  8-inch  lengths  of  wood 
|  inch  square.  Find  the  middle  of  each  piece  and  mark  a  cross-line  at 
this  point.  Draw  two  lines  parallel  to  this,  one  at  each  side  of  it,  TV  inch 
distant  from  it.  Saw  into  the  strip  on  each  of  these  two  lines,  cutting 
halfway  through  the  strip.  Cut  out  the  central  block.  The  two  strips 
may  now  be  put  together  at  right  angles  to  each  other,  the  space  formed 
by  cutting  out  the  block  fitting  over  the  remaining  section  of  the  other 
stick.  See  that  they  fit  well. 

28 


SOME  TOYS  THAT  WORK  BY  AIR  29 

With  a  knife  shave  off  the  opposite  angles  of  one  arm  until  a  thin  blade 
of  wood  is  left.  The  central  region  is  not  cut  away,  but  bevels  on  the  thin 
blade.  Cut  each  of  the  other  arms  in  the  same  way,  so  that  the  blades 
are  inclined  in  the  same  direction.  Fasten  the  mill  thus  formed  securely  to 
a  cylindrical  stick  somewhat  larger  than  a  pencil. 

The  base  of  the  windmill  is  built  thus:  Cut  a  3-inch  length  of  J-inch 
stuff  that  is  i  inch  wide.  At  each  end  with  small  brads  fasten  on  a  2-inch 
length  of  the  same  material  at  right  angles  to  the  3-inch  strip,  the  two 
shorter  strips  parallel  to  each  other  and  on  the  same  side  of  the  3-inch 
strip.  Bore  a  hole  near  the  top  of  each  2-inch  piece,  the  holes  in  line  so 
that  the  cylindrical  piece  fastened  to  the  windmill  may  be  run  through 
them.  Bore  a  hole  in  the  middle  of  the  3-inch  piece.  This  is  fastened  to 
the  upright  piece  which  should  be  f  inch  square  and  8  inches  long.  Cut  a 
thin  piece  of  wood  out  of  a  cigar  box  or  similar  material  to  form  the  vane 
of  the  mill.  Let  this  be  6  inches  long  and  4  inches  wide,  with  a  projecting 
piece  sticking  out  from  the  4-inch  side,  the  projection  to  be  i  inch  long 
and  J  inch  wide.  Tack  this  projection  to  the  3-inch  strip  that  makes  the 
base  of  the  structure  that  carries  the  mill  so  that  the  vane  projects  from 
the  base  in  a  vertical  plane  parallel  to  the  cylindrical  strip  that  serves  as 
the  axle  for  the  mill. 

When  this  vane  is  on  the  basal  strip,  fasten  the  base  to  the  upright  sup- 
port by  running  a  flat-headed  wire  nail  through  the  hole  bored  in  the  basal 
piece;  drive  it  in  through  the  center  of  the  end  of  the  supporting  upright. 
Put  the  axle  of  the  mill  through  the  holes  bored  in  the  supports  and  drive 
a  couple  of  small  brads  through  the  axle,  one  on  either  side  of  one  of  the 
supports,  so  that  the  mill  will  be  held  in  place. 

Gearing  for  work. — Put  a  spool,  like  a  small  silk  spool,  on  the  axle, 
so  that  it  will  serve  as  a  pulley  wheel,  on  which  a  string  belt  may  be  run 
to  couple  up  the  mill  with  any  piece  of  machinery  that  you  may  want  to 
run  with  wind  power.  The  machine  must  of  course  be  set  on  a  base  that 
will  revolve  with  the  mill. 

How  is  the  ordinary  windmill  attached  to  a  pump,  for  instance,  that 
the  connections  may  be  maintained  as  the  wind  veers? 

Cut  out  a  2-inch  circle  of  |-inch  wood,  or  a  section  from  a  large  spool. 
Fasten  this  eccentrically  to  one  end  of  the  axle.  Run  a  thin  strip  of  wood 
to  serve  as  driving  rod  from  this  to  work  a  wooden  doll  with  jointed  arms 
and  legs.  One  of  the  uprights  supporting  the  mill  may  be  lengthened  so 
that  the  figure  can  be  attached  to  it,  and  the  doll  will  dance  as  the  mill 
goes  around.  Other  contrivances  can  be  added  to  the  mill  and  pupils  may 
use  their  ingenuity  in  devising  such  attachments. 


30     ,  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Why  the  windmill  goes  around. — It  is  evident  that  the  force  of  the  wind 
blowing  against  the  diagonally  placed  arms  of  the  windmill  drives  the  wind- 
mill around.  If  the  arms  of  the  windmill  were  turned  so  that  the  wind 
struck  them  squarely  a  perpendicular  blow,  there  would  be  no  rotation  of 
the  mill;  the  wind  would  simply  tend  to  force  the  windmill  back  in  the 
direction  toward  which  the  wind  is  blowing.  But  with  the  arms  of  the  mill 
inclined  to  the  wind  so  that  the  wind  strikes  a  glancing  blow,  a  part  of  the 
pressure  acts  in  the  direction  of  the  rotation  of  the  mill.  In  other  words, 
the  wind  pressure  is  decomposed  into  elements,  one  of  which  serves  to 
drive  the  mill  around.  The  principle  involved  in  the  composition  or  de- 
composition of  forces  may  be  illustrated  by  the  following  experiment: 

An  experiment  showing  the  composition  or  decomposition  of  forces. — 
53.  Drive  three  tacks  into  the  top  of  a  table  or  in  the  floor,  at  the  points 
of  a  triangle,  each  side  of  which  is  at  least  two  feet  long.  By  means  of  a 
short  string  tie  the  ring  of  a  spring  balance  to  each  of  the  tacks.  Take 
three  strings  about  10  inches  long;  tie  the  three  together  by  a  single  knot 
at  the  ends  of  the  strings  leaving  three  free  ends.  Fasten  one  of  these 
free  ends  to  each  of  the  hooks  of  the  three  scale  balances.  In  tying  the 
strings  to  the  spring  balances,  make  the  length  of  the  string  short  enough 
so  that  each  balance  will  register  some  pull. 

It  is  evident  that  the  amount  registered  on  any  one  scale  is  the  resultant 
of  the  pulls  of  the  other  two;  that  is,  the  force  pulling  on  one  string  is 
equivalent  to  the  counter-pull  on  the  other  two. 

Graphic  calculation. — The  relation  between  these  forces  may  be  graphi- 
cally calculated  in  this  way: 

54.  Lay  a  good-sized  sheet  of  paper  on  the  table  underneath  the  three 
strings,  its  center  about  under  the  knot.  With  a  ruler  draw  lines  im- 
mediately under  and  parallel  to  the  three  strings,  the  three  lines  meeting 
in  a  point  immediately  under  the  central  knot.  Mark  beside  each  line  the 
amount  registered  by  the  corresponding  scale,  then  remove  the  paper. 
Suppose  one  scale  is  registering  6  ounces.  Measure  off  6  inches  from  the 
point  of  intersection  of  the  three  lines  along  the  line  that  led  to  this  scale 
and  mark  the  point.  Suppose  the  adjacent  scale  registered  8  ounces. 
Measure  off  and  mark  a  point  8  inches  distant  from  the  intersection. 
From  the  point  marked  on  the  first  line  draw  a  line  parallel  to  the  second ; 
and  similarly  from  the  point  marked  on  the  second  line  draw  a  line  parallel 
to  the  first,  the  two  lines  intersecting.  A  parallelogram  is  thus  drawn,  and 
the  third  line,  when  continued  through  the  point  of  intersection  of  the 
three  lines,  should  be  the  diagonal  of  the  parallelogram,  and  its  length  in 
inches  will  be  equal  to  the  number  of  ounces  registered  by  the  third  scale. 
Thus,  knowing  the  strength  and  direction  of  the  pull  of  two  combined 


SOME  TOYS  THAT  WORK  BY  AIR 


31 


forces,  the  resultant  may  be  determined;  or,  knowing  the  resultant  and  the 
direction  of  the  pull  of  the  component  forces,  the  latter  may  be  determined. 
Application  to  windmill. — To  apply  this  to  the  windmill,  suppose  that 
line  AB  in  the  diagram  (Fig.  6)  represents  the  end  of  the  blade  of  the 
windmill,  and  line  CD  represents  the  direction  of  the  wind,  and  its  length 
the  force  of  the  wind.  CE  will  represent  the  push  given  to  the  windmill 
to  cause  its  rotation.  The  other  factor  into  which  the  force  of  the  wind 
is  resolved  is  represented  by  the  line  CF;  and  the  parallelogram  of  forces 
is  completed  by  the  other  lines  of  the  figure.  Relative  lengths  of  the  lines 


FIG.  6. — Diagram  of  the  decomposition  of  the  force  of  the  wind  to  turn  the  mill. 
Note  that  the  sum  of  the  components  is  greater  than  the  original  force  of  the  wind. 
What  force  is  added  to  that  of  the  wind  to  make  the  kite  fly  (see  p.  34),  and  so  should 
be  considered  in  the  diagram  ?  Draw  a  diagram  like  this  one  and  add  this  other  force. 

CD  and  CE  are  entirely  hypothetical  and  will  of  course  have  to  be  deter- 
mined in  any  given  case  by  the  velocity  of  the  wind  that  is  blowing  and  by 
the  amount  of  friction  to  be  overcome  in  the  turning  of  the  windmill  and 
the  amount  of  work  that  the  mill  is  doing.  How  is  it  possible  for  the  sum 
of  the  two  elements  into  which  the  wind  is  decomposed  to  be  apparently 
greater  than  the  whole  force  of  the  wind? 

A  simple  flier. — 55.  That  the  push  of  the  air  on  the  blades  of  a  wind- 
mill develops  enough  force  to  lift  the  blade  if  it  is  free  to  move  is  shown 
by  this  simple  flier.  Cut  a  piece  of  wood  about  5  inches  long  and  i  inch  in 
diameter  to  serve  as  a  handle.  An  inch  from  one  end  make  a  circular  cut 
with  a  saw  and  then  cut  away  the  wood  so  as  to  leave  projecting  from  the 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


center  of  the  end  a  round  wooden  peg  an  inch  long  and  just  large  enough 
to  fit  loosely  into  the  hole  of  a  spool.  If  it  projects  beyond  the  spool  saw 
it  off  so  that  its  end  is  flush  with  the  end  of  the  spool.  Shape  the  handle 

now  so  that  it  can  be  held  comfortably  in  the 
£         left  hand.     Drive  two  brads  into  one  end  of 
lj          the  spool,  placing  them  on  opposite  sides  of  the 
central  hole,  and  let  their  heads  stick  up  about 
.B          i  inch.    Cut  from  light-weight  tin,  like  that  of 

5  a  tomato  can,  a  flier  shaped  like  a  pair  of  pro- 
peller blades  similar  to  this  pattern  (Fig.   7). 
Punch  two  holes  near  its  center  large  enough  to 

^         easily  slip  over  the  brads  on  the  end  of  the 
spool.     Twist  the  ends  of  the  blades  so  that 

O 

Z         they  are  inclined  to   the  central  portion  and 

6  curve  in  opposite  directions,  similar  to  the  wood 
propeller  of  the  aeroplane  (Fig.  9). 

Wind  a  yard  or  so  of  good  stout  string  on 
the  spool.  Set  it  on  the  peg  of  the  handle  and 
J  place  the  flier  on  the  end  of  the  spool,  the  brad 
|  heads  in  the  holes,  and  in  such  a  way  that 
I  when  the  string  is  pulled  so  as  to  whirl  the  spool 
$  rapidly  the  blades  will  cut  the  air  so  as  to 
.Jj  lift  the  flier  off  the  spool.  Grasp  the  handle  in 
m  the  left  hand,  flier  up;  with  the  right  hand  take 
%  hold  of  the  free  end  of  the  string  and  give  it  a 
''§,  strong  pull,  unwinding  it  all.  As  the  spool  re- 
a  volves  the  whirling  motion  is  imparted  to  the 

flier  and  it  rises  into  the  air. 

"%•  To  make  the  kite. — 56.    Cut   a   thin   strip 

of  bamboo,  or  other  light  wood,  3  feet  long. 
If  of  white  pine  or  cedar  make  it  about  J  inch 
square.  The  bamboo  may  be  even  thinner. 
Cut  a  second  piece  20  inches  long.  With  small 
>  brads  tack  the  shorter  piece  at  its  midpoint  on 
to  the  long  piece,  one  foot  from  one  end.  Bind 
the  joint  with  coarse  thread.  Tie  the  end  of  a 
piece  of  string  to  one  end  of  the  long  piece,  then 
fasten  it  tautly  to  one  end  of  the  short  piece, 
then  to  the  other  end  of  the  long  piece,  to  the 
other  end  of  the  short  piece,  and  fasten  it  at 
the  original  point  of  tie  at  the  end  of  the 


•§ 


SOME  TOYS  THAT  WORK  BY  AIR  33 

long  piece.  Thus  the  border  of  the  kite  is  outlined  in  tightly  stretched 
string.  The  sharpest  angle  marks  the  bottom  of  the  kite. 

Lay  the  kite  frame  down  on  a  piece  of  tissue  paper  (newspaper  will  do, 
or  strong  wrapping  paper  that  is  not  too  heavy) .  With  shears  cut  the  paper 
parallel  to  the  string,  about  2  inches  from  it  and  outside  of  the  string. 
Put  library  paste,  or  homemade  flour  paste,  on  this  projecting  2  inches, 
and  turn  it  over  the  string,  pressing  it  on  the  paper.  Let  it  dry. 

Tail  and  bridle. — Tear  some  old  cloth  up  into  inch-wide  strips  and  tie 
these  together  so  as  to  make  a  tail  about  12  feet  long.  Tie  one  end  of  this 
to  a  short  string  attached  to .  the  lower  point  of  the  kite.  Cut  a  strong 
string  30  inches  long,  and  tie  one  end  of  the  string  to  the  cross-piece  of 
the  kite,  8  inches  from  its  intersection  with  the  upright.  Pass  the  other 
end  of  the  string  through  a  small  hole  punched  in  the  paper  at  a  point 
just  above  this  tie  point.  In  a  similar  way  punch  a  hole  8  inches  from 
the  upright  on  the  opposite  side  of  the  kite,  so  that  the  other  end  of  the 
string  may  be  tied  to  the  cross-piece  in  corresponding  position.  On  the 
upright,  8  inches  above  its  intersection  with  the  cross-piece,  tie  one  end 
of  an  1 8-inch  string.  There  are  now  three  strands  of  string  tied  at  three 
points  of  the  kite.  Bring  these  together  and  knot  them  so  that  the  knot 
stands  directly  above  the  upright  and  so  that  when  the  kite  is  flying  it 
will  be  held  inclined  to  the  wind,  the  tail  end  of  the  kite  slanting  back- 
ward. This  arrangement  of  strings  is  called  the  bridle,  and  the  flight  of 
the  kite  depends  on  the  accuracy  with  which  it  is  adjusted.  The  string 
for  flying  the  kite  is  now  tied  at  the  point  of  the  bridle  where  the  three 
strands  intersect,  and  the  kite  is  ready  to  fly. 

Flying  the  kite. — One  person  holds  the  kite  in  the  right  hand,  the  fingers 
grasping  the  point  of  intersection  of  the  two  sticks.  The  kite  should  face 
the  wind.  The  second  person  lets  out  35  or  40  feet  of  string  and  prepares 
to  run  against  the  wind.  The  first  person  gives  the  kite  a  toss  into  the  air 
as  the  second  person  starts  to  run.  As  the  wind  catches  the  kite,  let  out 
more  string,  but  not  too  rapidly.  If  the  kite  tends  to  turn  somersaults, 
dashing  its  nose  into  the  ground,  it  needs  more  tail,  and  this  should  be 
added  until  it  flies  steadily. 

Bits  of  colored  paper  or  windmills  made  of  colored  paper  may  be 
slipped  on  the  string  to  blow  up  to  the  kite,  the  windmills  whirling  as  they 
go.  The  kite  may  be  ornamented  with  a  face  drawn  upon  it  in  bold  out- 
lines so  that  it  is  visible  when  it  is  flying. 

57.  A  bow  kite  is  made  by  taking  a  straight  upright  24  inches  long 
as  before  and  fastening  to  its  top  nearly  half  of  a  barrel  hoop  shaved  down 
so  that  it  is  J  inch  square.  This  is  fastened  at  its  midpoint  to  the  top  of 
the  upright,  the  curve  of  the  bow  in  a  plane  at  right  angles  to  the  upright. 


34  GUIDE  IN  PHYSICAL  NATURE-STUDY 

A  string  runs  from  one  end  of  the  hoop  to  the  opposite  end,  thence  to  the 
lower  point  of  the  upright  and  back  again  to  the  first  point.  The  tissue 
paper  is  pasted  on  as  before,  but  loosely,  and  since  the  kite  frame  will  not 
lie  flat  it  must  be  pasted  to  one  side,  then  rolled  over  to  be  pasted  to  the 
opposite  side.  It  is  also  pasted  over  the  hoop.  This  kite  flies  without  a 
tail,  the  convex  side  toward  the  wind;  the  string  is  attached  at  a  point  on 
the  upright  8  inches  below  its  top. 

For  making  the  box  kite. — 58.  Out  of  pine,  spruce,  or  cedar,  that  is 
free  from  knots,  cut  four  pieces  of  f-inch  stuff  32  inches  long,  four  18  inches 
long,  four  9  inches,  and  four  20  inches.  Fasten  two  of  the  32-inch  strips 
and  two  of  the  i8:inch  strips  together,  so  as  to  make  a  rectangle,  the  short 
strips  between  the  long  ones.  Do  the  same  with  the  other  pair  of  32-inch 
and  1 8-inch  strips.  Cut  two  strips  of  cambric  10  inches  wide  and  55  inches 
long.  Sew  the  ends  of  these  together,  overlapping  i  inch,  thus  making 
two  lo-inch  bands  of  the  material.  Lay  the  two  rectangles  made  out  of 
the  wood  strips  together  so  that  they  coincide,  and  put  one  of  the  cloth 
bands  around  each  end,  the  bands  on  the  outside  of  the  wood  rectangles. 
Spread  the  rectangles  apart,  thus  stretching  the  cloth  bands,  insert  the 
g-inch'  strips  between  the  corners  of  the  rectangle,  and  brace  them  to  pre- 
vent their  collapse  with  the  20-inch  strips,  the  latter  crossing  each  other 
diagonally.  Cut  some  J-inch-wide  strips  of  light  tin  to  bind  on  and  rein- 
force the  corners. 

The  bridle  for  this  kite  is  made  by  fastening  a  3o-inch  piece  of  string, 
tying  one  end  just  below  the  band  to  one  of  the  3 2 -inch  strips  and  the 
other  at  the  opposite  side  of  the  same  large  rectangle,  close  to  the  same 
border  of  the  cloth  band.  The  string  for  flying  is  tied  to  the  midpoint  of 
this  bridle.  The  box  kite  flies  without  a  tail. 

Why  the  kite  flies. — It  is  very  evident  that  the  kite  is  kept  up  by  the 
force  of  the  wind.  The  wind  of  course  is  blowing  horizontally,  that  is, 
parallel  to  the  surface  of  the  earth.  The  kite  tends  to  fall  directly  down, 
pulled  by  the  force  of  gravity.  In  some  way  the  wind  blowing  horizontally 
is  made  to  overcome  this  pull  of  gravity  and  so  keep  the  kite  in  the  air. 
When  the  kite  is  flying  it  will  be  noted  that  the  kite  is  inclined  to  the 
direction  of  the  wind,  so  that  the  wind  strikes  the  face  of  the  kite  a  glancing 
blow.  The  string  serves  to  hold  the  kite  in  a  fixed  position.  The  force  of 
the  wind  is  broken  into  components  in  much  the  same  way  that  the  force 
of  the  wind  is  broken  in  running  the  windmill.  59.  Draw  a  diagram  that 
will  show  the  elements  involved  and  how  the  wind  pressure  is  decomposed 
into  two  elements,  one  of  which  overcomes  the  force  of  gravity  and  keeps 
the  kite  in  the  air.  Why  will  the  kite  not  fly  except  when  it  is  held  by 
the  string? 


SOME  TOYS  THAT  WORK  BY  AIR  35 

To  make  an  aeroplane. — 60.  A  simple  but  very  effective  type  of  aero- 
plane is  made  as  follows:  Cut  a  f-inch  square  strip  of  white  pine  22 
inches  long  (or  use  a  piece  of  bamboo  f  inch  wide).  This  strip  should  be 
straight-grained  and  free  from  knots,  for  it  serves  as  the  backbone  of  the 
machine  and  must  bear  the  strain  of  the  twisted  rubber  bands  that  serve 
to  run  the  propeller. 

Cut  a  strip  of  tin  4§  inches  long  and  f  inch  wide.  Bend  it  2  inches 
from  one  end  into  a  sharp  V.  Holding  it  with  the  long  arm  to  the  left 
bend  this  long  arm  i  inch  from  its  end  so  that  the  bent  portion  turns  to 
the  right  and  lies  at  right  angles  to  the  rest  of  this  side  of  the  V.  Bend  the 
other  arm  of  the  V  in  the  same  direction  i  inch  from  its  end  so  that  the 
bent  portion  is  parallel  to  that  of  the  first  arm  of  the  V.  These  two  parallel 
parts  are  now  to  be  bound  tightly  with  coarse  linen  thread  to  the  end  of 
the  backbone,  their  long  axes  coincident  with  its  long  axis.  This  end  is 
the  front  end  of  the  machine.  Near  the  tip  of  this  V  and  in  its  midline 
punch  a  hole  through  both  sides  so  that,  a  stiff  wire  axle  that  bears  the 
propeller  may  run  through  the  hole  parallel  to  the  long  axis  of  the  backbone. 

The  skids. — -Cut  two  thin  strips  of  bamboo  |  inch  wide  and  6  inches 
long  and  one  4^  inches  long.  Bind  these  together  with  the  linen  thread 
in  the  form  of  a  triangle  letting  their  ends  overlap  J  inch.  Bind  this  to 
the  backbone  i  inch  back  of  the  tin  propeller  bearing,  the  juncture  of  the 
two  long  sides  above  the  backbone  and  on  the  opposite  side  from  the 
point  of  the  tin  strip.  Let  the  plane  of  the  triangle  be  at  right  angles  to 
the  backbone.  Cut  two  more  such  thin  strips  5  inches  long  and  bind  one 
end  of  one  to  the  midpoint  of  one  of  the  long  sides  of  the  triangle,  the 
other  end  to  the  backbone  about  2\  inches  back  of  the  point  to  which 
the  apex  of  the  triangle  is  affixed.  The  other  strip  will  be  bound  to  brace 
the  other  side  of  the  triangle  in  a  similar  way. 

Cut  two  more  thin  strips  5  inches  long.  Set  one  on  each  side  of  the 
backbone  i  inch  from  its  rear  end  at  right  angles  to  the  backbone  and 
perpendicular  to  the  base  of  the  forward  triangle.  Bind  them  on  tightly 
at  their  midpoints.  Fasten  a  brace  of  bamboo  from  the  upper  end  of  this 
pair  of  strips  to  the  backbone  about  3  inches  in  front  of  the  point  where 
the  pair  of  5-inch  strips  is  bound  to  it. 

Cut  three  strips  of  bamboo  3  inches  long  and  so  thin  that  each  can  be 
bent  into  a  U  over  the  end  of  the  finger  without  breaking.  Bind  one  of 
these  by  its  ends  to  the  lower  end  of  each  side  of  the  bamboo  triangle  and 
one  to  the  lower  end  of  this  last  support  near  the  rear,  the  plane  of  each  U 
parallel  to  the  longitudinal  axis  of  the  backbone.  These  three  loops  form 
skids  on  which  the  aeroplane  stands  and  they  slip  along  the  floor  or  side- 
walk as  the  machine  takes  flight  (Figs.  8  and  9). 


36  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Propeller. — Shape  a  g-inch  propeller  out  of  the  tin  of  a  coffee  can  similar 
to  the  one  cut  for  the  flier  (p.  32).  If  the  longitudinal  axis  of  the  propeller 
is  made  to  coincide  with  the  length  of  the  can  the  curve  of  the  tin  will 
give  about  the  right  curve  to  the  propeller  after  it  is  bent  according  to  the 
instructions  there  given.  Or  a  propeller  may  be  fashioned  out  of  white 
pine,  white  wood,  or  cedar  that  is  straight-grained  and  free  from  knots. 
Cut  the  block  of  |-inch  stuff  9  inches  long  and  2  inches  wide.  Bore  a  hole 
at  the  middle  of  one  broad  face  just  large  enough  to  take  the  stiff  wire 
that  must  be  used  as  the  axle  for  the  propeller.  Draw  a  square  i  inch  on 


FIG.  8. — The  aeroplane  frame.  (In  this  the  forward  legs  are  part  of  a  quadrangular 
frame  instead  of  a  triangular  one  as  described.) 

each  side,  its  center  coincident  with  the  hole,  its  sides  parallel  to  the  sides 
and  ends  of  the  block.  Draw  lines  from  its  corners  to  points  on  the  adjacent 
sides  2  inches  from  each  corner  of  the  block.  Cut  away  the  sides  of  the 
block  along  these  lines.  Mark  the  ends  of  the  block  according  to  the 
diagram  (Fig.  10)  and  saw  away  the  wood  from  both  sides  of  the  diagonal 
strip  down  to  the  central  square.  By  sandpaper  held  over  the  thumb  to 
give  a  curved  surface  or  with  bits  of  broken  glass  having  rounding  edges 
work  away  the  wood  of  the  blades  to  make  them  thin  and  curved  according 
to  the  heavy  line  of  the  diagram.  The  blades  may  be  shaped  so  that  their 
outlines  are  similar  to  these  of  the  flier.  Cut  away  the  corners  of  the  central 
block  so  that  it  joins  the  blades  in  flowing  surfaces. 

Pass  one  end  of  a  6-inch  length  of  stiff  wire  through  the  hole  in  the 
center  of  the  propeller  so  that  it  protrudes  f-inch.  Bend  this  protruding 
end  down  to  the  wood  center  and  tack  it  securely.  If  the  tin  propeller 
is  to  be  used  stick  the  wire  through  one  hole  ij  inches,  bend  it  so  that  the 
end  can  be  thrust  back  through  the  other  hole  and  twisted  on  the  long  wire 
so  as  to  hold  the  propeller  securely.  A  short  block  of  wood  set  on  the  back 


SOME  TOYS  THAT  WORK  BY  AIR 


37 


of  the  propeller  between  the  holes  and  included  in  the  loop  of  wire  will 
help  to  hold  the  propeller  solidly. 

Put  a  flat  good-sized  bead  on  the  free  end  of  the  wire,  then  pass  the 
end  through  the  holes  in  the  tin  propeller  bearing  and  make  a  triangular 
loop  on  the  wire  just  back  of  the  ^bearing  to  take  the  strands  of  rubber 
that  make  the  motor.  The  bead  used  helps  to  reduce  friction.  Make 
another  small  triangle  of  wire  and  bend  the  free  ends  so  that  they  can  be 
bound  securely  to  the  front  of  the  rear  skid  strut  about  i  inch  from  the 


FIG.  9. — Front  view  of  frame  and  propeller 

backbone.  Pass  the  long  strand  of  rubber  that  can  be  bought  for  this 
purpose  through  this  rear  wire  loop,  then  through  the  one  on  the  rear 
end  of  the  propeller  shaft,  and  so  back  and  forth  until  about  ten  strands 
are  laid  on.  Tie  the  ends  of  the  rubber  together  to  complete  the  last  strand. 
Planes. — Cut  two  thin  bamboo  strips  f  inch  wide  and  22  inches  long 
and  two  5  inches  long,  and  bind  their  crossed  ends  together  so  as  to  make  a 
rectangular  parallelogram  of  the  strips  that  will  serve  as  the  frame  for  the 
forward  plane.  In  the  same  way  make  the  rear  frame  for  the  plane  10  by  4 \ 
inches.  Cover  the  frames  with  strong  but  light  paper,  folding  the  paper 
over  the  edge  of  the  frame  i  inch  and  gluing  it  down.  Fasten  the  forward 
plane  horizontally  to  the  backbone,  its  long  axis  at  right  angles  to  the 
latter,  its  front  edge  just  back  of  the  struts  that  support  the  forward  skids. 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


Tack  it  lightly  in  place  with  thread.  The  rear  plane  is  fastened  similarly 
with  its  hind  edge  just  in  front  of  the  brace  that  supports  the  rear  strut. 
When  the  planes  are  in  place  balance  the  machine  on  the  forefinger  placed 

under  the  backbone  near  its  center. 
If  the  planes  do  not  lie  horizontally 
but  tend  to  dip  to  one  side  or  the 
other  their  position  may  need  to  be 
changed  slightly.  When  they  do 
balance  well  fasten  them  securely  in 
place,  daubing  the  bindings  with 
glue  so  that  they  will  not  slip.  Guy 


FIG.  10. — Diagram  of  end  of  block, 
showing  method  of  cutting  and  curve  of 
blade  of  wood  propeller  for  aeroplane. 


threads  may  then  be  run  from  the 
outer  tips  of  the  planes  to  the  ad- 
jacent struts  to  help  hold  them  in  place  (Fig.  n). 

Observe  which  way  the  propeller,  which  is  at  the  front  of  the  machine, 
should  turn  in  order  to  carry  the  machine  in  the  air,  then  turn  it  about 


FIG.  1 1 . — The  aeroplane  complete 

150  times  in  the  opposite  direction.  Head  the  aeroplane  into  the  wind, 
set  it  down  on  a  smooth  surface,  like  a  cement  sidewalk,  release  the  pro- 
peller and  it  should  rise  and  fly.  If  at  first  it  is  not  successful  try  shifting 
the  planes  slightly  forward  or  back  or  changing  their  inclination.  Possibly 
you  can  reduce  the  weight  of  the  machine.  It  is  imperative  to  keep  in 
mind  while  building  the  aeroplane  that  it  must  be  exceedingly  light  in 
order  to  fly  and  that  the  parts  must  not  be  made  any  heavier  than  is  abso- 
lutely necessary. 

Another  model. — 61.  A  still  larger  aeroplane  with  two  propellers  is 
made  by  making  a  triangular  frame  of  f-inch  square  strips  42  inches  long 
with  a  lof-inch  strip  of  the  same  stuff  for  the  base  of  the  triangle.  The 


SOME  TOYS  THAT  WORK  BY  AIR  39 

apex  of  the  triangle  is  in  this  case  to  be  the  front  end  of  the  plane  and  is 
provided  with  a  pair  of  hooks  to  take  the  rubber  bands,  one  set  of  which 
runs  along  under  each  long  side  to  the  propeller  bearing  at  its  hind  end. 
The  forward  plane  is  small,  about  12  by  4  inches,  and  is  fastened  in  the 
plane  of  the  triangle  about  6  inches  back  of  its  tip,  its  longitudinal  axis 
perpendicular  to  the  altitude  of  the  triangle.  The  rear  plane  is  36  by  5 
inches  and  attaches  in  a  similar  position  6  inches  from  the  hind  end  of  the 
triangular  frame.  This  plane  takes  two  Q-inch  propellers.  If  the  pull  of 
the  tightly  twisted  rubber  bands  tends  to  bend  the  long  sides  of  the  triangle, 
run  fine  wires  one  from  the  rear  of  each  side  to  the  apex  of  the  triangle 
over  a  2-inch  upright  of  light  stuff  set  on  the  middle  of  each  side  and  bound 
in  place.  Skids  may  be  provided  as  in  the  other  plane,  but  they  are  not  as 
necessary,  for  this  plane  is  started  off  from  the  hands,  each  hand  holding 
one  propeller  and  letting  go  as  the  plane  is  launched  by  a  shove  out  from 
the  shoulders  as  the  person  launching  it  stands  upright. 

62.  A  very  simple  aeroplane  propelled  from  a  sling  shot  instead  of  by 
a  propeller,  is  made  thus:  Split  a  J-inch  square  wood  strip,  10  inches  long, 
at  one  end.  Insert  a  light  card  i  J  by  3  inches  so  that  the  ends  of  the  card 
stick  out  equally  on  either  side  of  the  stick  and  its  rear  edge  is  i|  inches 
from  the  end  of  the  stick.  Bind  it  in  place.  Tack  another  card  on  the 
stick,  the  same  size  as  this,  its  surface  at  right  angles  to  the  first,  its  rear 
edge  at  the  end  of  the  stick,  its  ends  projecting  equally  from  the  sides  of 
the  stick.  Parallel  to  this  card,  at  the  other  end  of  the  stick,  fasten  one 
8  by  ij  inches,  its  middle  on  the  stick.  Notch  the  stick  under  this  near 
the  end.  Bend  a  piece  of  telephone  wire  in  the  form  of  a  Y.  Tie  one  end 
of  a  rubber  band  to  the  tip  of  each  arm  of  the  Y.  Tie  one  end  of  a  6-inch 
string  to  the  free  end  of  one  band,  the  other  end  to  the  other  band.  Hold 
the  base  of  the  Y  in  the  left  hand.  Hold  the  aeroplane  by  the  end  near 
the  small  cards,  between  thumb  and  finger  of  the  right  hand,  the  string 
of  the  sling  in  the  notch  near  the  front  end.  Pull  it  back,  stretching  the 
rubbers,  and  release  it  for  its  flight. 

To  make  and  operate  a  sailboat. — The  sailboat  is  another  thing  that, 
like  the  aeroplane,  kite,  and  windmill,  depends  on  the  decomposition  of  the 
force  of  the  wind  for  its  propulsive  power.  Both  sailboat  and  windmill  are 
very  old  contrivances.  A  very  simple  sailboat  may  be  made  with  little 
trouble.  63.  Take  a  block  of  f-inch  stuff  6  inches  long  and  3  inches  wide. 
Draw  a  line  down  the  middle  of  one  broad  side.  Mark  points  on  this  line 
i  J,  2  J,  and  3!  inches  from  one  end.  Draw  cross-lines  at  these  points  at  right 
angles  to  the  central  line.  Mark  off  on  either  side  of  the  central  line  on 
the  first  of  these  cross-lines  points  i  inch  from  the  central  line,  on  the  second 
and  third  i  J  inches,  and  at  the  rear  end  of  the  block  points  i  J  inches  from 


4o 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


the  center.  Connect  these  points  with  flowing  lines  to  mark  the  sides  of 
the  boat.  Then  with  a  sharp  knife  cut  along  these  lines  to  shape  the  boat. 
Cut  a  thin  strip  of  wood  6  inches  long  and  i  inch  wide.  Fasten  this  on 
edge  with  brads  along  the  midline  of  the  bottom  of  the  boat  to  serve  as  a 
keel.  On  the  opposite  side  from  the  keel,  the  deck  of  the  boat,  bore  a  hole 
in  the  midline  ij  inches  from  the  prow  of  the  boat  and  set  tightly  in  this 
a  round  stick  5  inches  long  and  about  J  inch  in  diameter  for  the  mast. 

Cut  out  a  rudder  shaped  as  in  Figure  1 2  and  fasten  it  vertically  in  the 
midline  at  the  stern  of  the  boat  with  two  double-pointed  tacks  set  about 

the  round  rudder  post  just  tightly  enough  so 
that  the  rudder  may  be  turned  into  the  desired 
position  but  still  held  in  place  when  so  set. 
The  blade  of  the  rudder  should  be  under  water 
when  the  boat  is  floating. 

Across  the  stern  of  the  boat  set  a  stiff  wire 
so  that  it  lies  parallel  to  the  deck  and  about 
|  inch  above  it,  the  ends  of  the  wire  bent  down 
and  fastened  on  either  side  by  means  of  tacks. 
The  sail. — To  make  the  sail  cut  a  piece  of 
cloth  4!  inches  long  at  its  lower  edge,  which 
fastens  to  the  boom;  3^  inches  long  on  the  side 
next  to  the  mast,  which  side  is  at  right  angles 
to  the  lower  edge;  2\  inches  long  on  its  upper 
edge,  which  lies  at  an  angle  of  45°  to  the  edge 

next  the  mast,  thus  making  the  edge  opposite  the  mast  about  6  inches  long. 
Turn  in  and  hem  down  \  inch  all  around  the  sail. 

Cut  two  round  sticks  T\  inch  in  diameter,  5  inches  and  2  J  inches  long, 
respectively.  Bind  a  round  loop  of  stiff  wire  on  one  end  of  each  of  these 
spars,  large  enough  to  slip  readily  over  the  mast.  Sew  these  spars  to  the 
lower  and  upper  edges  of  the  sail  by  looping  the  thread  over  the  spar  at 
each  stitch.  Slip  the  wire  loops  on  the  ends  of  the  spars  over  the  mast, 
the  long  spar  next  the  deck.  Tie  one  end  of  a  short  string  to  the  tip  of  the 
upper  spar  and  an  end  of  another  string  at  its  base  near  the  ring  of  wire. 
Tie  the  other  ends  of  these  strings  to  the  upper  end  of  the  mast  so  that 
the  sail  will  be  hung  with  its  long  spar  or  boom  about  \  inch  above  the 
deck/ 

Tie  one  end  of  a  5-inch  string  to  the  outer  end  of  the  boom  and  fasten 
the  other  end  loosely  to  the  wire  at  the  stern  of  the  boat,  which  is  ready  to 
sail  now.  It  is  well  to  keep  a  long  string  tied  to  the  stern  of  the  boat  while 
sailing  it  until  you  have  mastered  the  art  of  adjusting  sail  and  rudder 
sufficiently  well  to  make  sure  that  the  boat  will  arrive  at  the  desired  port 


FIG.  12. — Rudder  of  sailboat 


SOME  TOYS  THAT  WORK  BY  AIR  41 

when  it  is  started  off  on  a  voyage.  Set  the  rudder  in  various  positions 
until  you  learn  what  its  effect  is  on  the  movements  of  the  boat.  The 
length  of  string  between  the  end  of  the  wire  and  the  tip  of  the  boom  must 
be  varied  according  to  the  direction  of  the  wind  in  relation  to  the  course 
of  the  boat.  You  may  readily  figure  out  these  things,  keeping  in  mind  the 
principle  of  the  composition  of  forces.  Can  a  boat  ever  sail  faster  than 
the  rate  at  which  the  wind  is  blowing? 

Sailors  in  the  olden  times  found  it  necessary  to  wait  for  a  favoring 
wind,  one  going  in  the  general  direction  which  they  wished  to  pursue  in 
their  journey.  But  the  modern  sailor  has  learned  how  to  tack  into  the 
teeth -of  the  wind.  How  close  to  the  wind  can  you  make  your  boat  sail? 

The  motor  boat. — 64.  The  sailboat  may  be  transformed  to  a  motor 
boat  or  a  motor  boat  may  be  built  on  the  same  lines  as  the  sailboat  just 
described.  The  motor  boat  needs  no  sail  or  mast.  Cut  the  keel  away 
from  in  front  of  the  rudder  for  a  space  of  i  inch,  and  slope  it  from  this 
point  to  the  front  of  the  boat,  where  it  may  be  J  inch  high.  Carefully 
punch  four  or  five  small  holes  in  the  keel  near  its  stern  end,  and  by 
means  of  strong  thread  or  fine  wire  run  through  these  holes  bind  to  the 
keel  at  the  stern  end  a  short  piece  of  glass  tubing,  the  ends  of  which 
have  been  heated  enough  in  the  flames  to  melt  down  their  sharp  edges 
and  leave  them  rounded.  A  small  piece  of  brass  tubing  may  be  used  in 
place  of  the  glass  or  a  small  screw-eye  may  be  set  in  the  keel  at  its  stern 
end.  Drive  a  brad  into  the  keel  at  its  front  end,  leaving  the*  head  project- 
ing so  that  the  rubber  band  for  motive  power  may  be  attached  to  it. 

Propeller. — Cut  two  pieces  of  tin  like  the  flier  on  page  32,  only  make 
these  smaller,  about  2  inches  long.  Lay  one  on  top  of  the  other  in  the 
form  of  a  cross  with  equal  arms.  Punch  two  holes  in  their  common  center 
and  wire  them  together  with  one  end  of  a  stiff  wire  set  through  the  holes 
and  twisted  to  fasten  them,  leaving  the  other  end  of  the  wire  projecting 
several  inches  from  their  midpoint  at  right  angles  to  the  plane  in  which 
they  lie.  Bend  the  blades  of  this  propeller  so  that  they  will  be  inclined 
like  the  vanes  of  the  windmill.  Thus  all  of  them  will  exert  their  thrust  in 
the  same  direction  when  the  propeller  is  turned  in  the  water. 

Slip  on  the  wire  a  rather  flat  glass  bead  of  about  the  same  diameter  as 
the  outside  of  the  glass  tubing  on  the  keel,  pass  the  wire  through  the  tube 
from  the  stern  end  forward.  Make  a  loop  on  the  wire  just  in  front  of  the 
tube  and  cut  off  the  excess  wire.  Fasten  the  ends  of  several  4-inch  rubber 
bands  to  this  wire  loop  and  their  other  ends  to  a  similar  wire  loop  that  is 
attached  firmly  to  the  brad  at  the  bow  end  of  the  keel. 

Turn  the  propeller  wheel  many  turns  until  the  rubber  bands  are  tightly 
twisted.  (Figure  out  in  which  direction  they  must  be  twisted  to  drive 


42  GUIDE  IN  PHYSICAL  NATURE-STUDY 

the  boat  forward  as  the  propeller  is  turned  by  their  untwisting.)  When 
the  boat  is  set  in  the  water  and  the  propeller  released  it  should  move  with 
considerable  speed. 

The  boat,  for  the  making  of  which  directions  have  been  given,  is  not 
a  very  graceful  model.  One  worked  out  of  a  thicker  block  of  wood  with 
curving  sides  instead  of  straight  and  with  a  hold  hollowed  out  of  the  block 
is  much  more  shipshape.  But  this  is  a  good  first  model  to  attempt.  The 
boy  or  girl  who  wants  to  make  a  better  type,  a  real  racing  motor  boat  or 
a  speedy  sailboat  with  more  elaborate  rig  and  numerous  sails,  may  consult 
such  books  as  those  on  boats  given  in  the  Appendix. 

To  make  a  water  wheel  and  use  it. — 65.  Cut  four  strips  from  a  cigar- 
box  cover  5  inches  long  and  f  inch  wide.  At  the  center  of  each  bore  a 
^-inch  hole  with  a  bit  and  brace.  Fasten  two  of  these  together  at  right 
angles  to  each  other  tacking  them  with  small  brads,  thus  making  a  cross 
with  a  hole  at  its  center.  Fasten  the  other  two  together  in  the  same  way. 
Cut  four  more  strips  if  inches  wide  and  3  inches  long  for  the  paddles. 
Fasten  one  of  these  to  the  edges  of  corresponding  arms  of  the  foregoing 
crosses,  its  long  edge  flush  with  the  end  of  the  arms,  the  short  edge  flush 
with  the  f-inch  outer  face  of  the  arm.  Fasten  the  other  three  in  corres- 
ponding positions  on  the  other  arms.  Make  a  round  axle  slightly  more 
than  J  inch  in  diameter  and  6  inches  long.  Force  it  into  the  holes  of  the 
two  crosses  and  let  it  stick  out  on  either  side  of  the  wheel.  Cut  two  up- 
rights of  the  cigar-box  wood  i  inch  wide  and  5  inches  long.  A  half-inch 
from  the  end  of  each  of  these  latter  and  in  the  midline  have  a  -jVinch 
hole.  Put  the  axis  into  these  holes  and  tack  the  uprights  to  the  end  of  a 
fooard  4  inches  wide.  Set  the  board  in  the  sink  and  let  the  water  from  the 
faucet  strike  the  paddles. 

Fasten  a  small  spool  to  one  of  the  projecting  ends  of  the  axle.  Make 
this  serve  as  a  wheel  over  which  a  loop  of  string  may  be  run  as  a  belt  to 
connect  with  any  mechanical  toy  and  furnish  the  power  for  its  propulsion. 
At  what  angle  will  the  water  strike  the  paddle  when  it  exerts  its  greatest 
force  in  turning  the  wheel  ?  How  is  a  water  turbine  built  ? 


TOP,  SLING,  AND  BOW 

To  make  and  spin  tops. — 66.  Saw  the  beveled  end  off  of  a  spool. 
Whittle  out  a  peg  long  enough  to  stick  through  this  and  project  J  inch 
below  the  bevel  and  i  inch  above  the  flat  side  of  the  spool  end.  Make 
the  peg  round  and  large  enough  to  fit  the  hole  of  the  spool  end  snugly. 
Drive  it  into  the  hole,  thus  making  the  top.  Hold  the  blunt  end  of  the 
peg  between  thumb  and  finger  and  give  it  a  vigorous  whirl,  letting  go  so 
that  the  top  will  drop  on  the  sharp  end  of  the  peg  and  keep  turning.  Make 
a  hemispherical  hole  in  the  middle  of  a  soft  pine  board  by  pounding  in 
the  head  of  a  brass  upholstery  tack.  Set  the  top  spinning  in  this  depression. 
Then  incline  the  board.  Does  the  top  incline  too  or  remain  upright  ?  Why  ? 

The  peg  top.— The  ordinary  wooden  peg  top  is  so  cheaply  bought  at 
the  store  that  it  is  not  worth  while  to  make  one.  67.  To  spin  such  you 
first  loop  one  end  of  the  string  around  the  upper  end  of  the  top,  .then  carry 
it  to  the  peg,  and  wind  it  on  firmly  over  the  loop  of  string  first  made,  up  to 
the  beginning  of  the  curved  portion.  Hold  the  top  in  the  hand  with  the 
peg  on  the  ball  of  the  thumb,  the  upper  end  of  the  top  covered  by  the 
first  three  fingers.  The  end  of  the  string  has  a  button  on  it  and  this  end 
is  held  between  the  first  and  second  fingers,  the  button  on  the  back  of  these 
fingers.  Throw  the  top  down  on  the  ground  with  an  overhand  throw  as 
if  the  top  were  a  ball.  The  string  unwinding  sets  it  spinning,  and  it  con- 
tinues to  spin  after  it  strikes  on  its  peg  end.  The  instructions  seem  easy, 
but  you  may  have  to  practice  some  time  before  you  acquire  the  art  of 
spinning  a  top. 

Inertia. — Can  you  balance  a  top  on  its  peg  when  it  is  not  spinning? 
What  happens  when  it  ceases  to  spin?  The  top  illustrates  beautifully  a 
law  of  motion,  namely  that  when  a  body  is  once  in  motion  it  tends  to  remain 
moving  in  the  same  line  or  plane  unless  some  force  is  used  to  change  the 
direction  of  its  motion.  If  a  very  heavy  disk  is  made  to  spin  it  requires  a 
very  great  force  to  move  it  out  of  the  plane  in  which  it  is  whirling.  Such 
whirling  disks  are  used  to  keep  boats  steady  so  they  will  not  rock  in  a  sea 
and  to  keep  the  car  upright  on  the  rail  in  the  monorail  railroads. 

The  top  on  a  tight  rope. — 68.  Get  the  spinning  top  on  the  palm  of 
your  hand;  you  can  scoop  it  up  while  it  is  spinning,  spreading  your  fingers 
so  that  it  will  climb  up  on  your  hand  over  the  web  between  the  second 
and  third  fingers.  While  holding  it  as  it  spins  incline  your  hand.  Does  it 
remain  upright?  While  it  spins  on  your  right  hand  hold  the  string  with 

43 


44  GUIDE  IN  PHYSICAL  NATURE-STUDY 

the  button  between  the  second  and  third  fingers  of  the  right  hand.  Hold 
most  of  the  string  in  the  left  hand,  but  have  a  couple  of  feet  of  it  stretched 
between  the  hands.  Then  incline  the  hand  so  that  the  top  will  spin  off 
on  the  string,  the  left-hand  end  of  which  is  somewhat  lower  than  the  right. 
Let  the  side  of  the  peg  be  supported  by  the  string  not  its  tip.  The  top 
will  spin  along  the  string,  standing  out  in  a  nearly  horizontal  position 
without  falling,  because  a  body  in  motion  resists  being  pulled  out  of  the 
plane  in  which  it  is  moving.  Thus  the  top,  while  spinning,  apparently 
defies  gravitation. 

The  sling.— 69.  Fill  a  pail  partly  full  of  water.  Hold  it  in  the  hand, 
arm  down,  then  swing  it  rapidly  with  a  full  arm  swing  over  the  head  and 
to  its  first  position.  Swing  it  several  times.  Why  does  not  the  water 
spill  out  when  the  pail  is  upside  down  over  the  head?  When  a  wagon  or 
carriage  is  being  driven  rapidly  over  a  muddy  road  in  what  direction  does 
the  water  fly  off  the  wheels  and  why? 

The  force  illustrated  in  the  foregoing  experiment  with  the  pail  is  utilized 
in  a  very  old  weapon,  the  sling.  70.  Cut  a  piece  of  leather  2  inches  wide 
and  5  inches  long.  Make  a  hole  in  the  middle  of  each  end  near  the  edge, 
large  enough  to  fasten  in  a  string.  Cut  two  limp  strings  one  2  feet,  the 
other  2\  feet  long.  Tie  one  end  of  the  string  to  the  leather  at  one  hole, 
an  end  of  the  other  into  the  other  hole.  Wrap  the  free  end  of  the  longer 
string  about  the  third  and  fourth  fingers  of  the  right  hand  a  couple  of 
times.  Hold  the  free  end  of  the  other  string  between  thumb  and  first 
finger  and  place  a  good-sized  pebble  in  the  leather.  When  the  arm  is 
hanging  free  at  the  side  the  leather  with  its  contained  stone  should  be 
just  off  the  ground.  Swing  the  sling  around  and  around  the  head  rapidly, 
then  suddenly  let  go  the  string  between  thumb  and  first  finger  when  you 
think  the  position  is  about  right  to  send  the  stone  toward  the  object  at 
which  it  is  aimed.  Some  practice  will  be  required  to  gain  skill  in  throwing 
the  stone  in  the  right  direction,  and  it  is  well  to  practice  in  the  open,  away 
from  windows  and  people. 

Centrifugal  force. — Sometimes  flywheels  or  grindstones  break  while 
in  motion.  How  do  the  fragments  fly?  How  does  the  cream  separator 
work?  Which  way  do  you  lean  in  riding  a  bicycle  around  a  corner  and 
why?  How  do  you  play  crack-the-whip  and  on  what  does  the  game  depend 
for  the  fun  in  it? 

To  make  bow  and  arrow. — 71.  Select  a  piece  of  wfell- seasoned  white 
cedar  or  arbor  vita  that  is  straight-grained,  i  inch  wide,  \  inch  thick,  and 
4  feet  long,  or  use  oak,  hickory,  ash,  Osage  orange.  Round  off  the  middle 
6  inches  and  then  round  off  the  rest,  tapering  to  each  end.  Make  the  ends 
about  \  inch  in  diameter.  Trim  each  end  and  cut  a  groove  in  it  to  hold 


TOP,  SLING,  AND  BOW  45 

the  cord.  Tie  a  permanent  loop  in  each  end  of  a  stout  cord  large  enough 
to  slip  over  the  tip  and  lie  in  the  groove.  Make  the  cord  with  its  loops 
about  2  inches  less  than  4  feet  long.  To  string  the  bow  slip  one  loop 
over  the  end  and  past  the  groove,  the  other  loop  over  the  other  end  and 
into  the  groove.  Set  this  end  of  the  bow  on  the  ground.  Press  the  knee 
against  the 'bow,  held  nearly  upright  by  the  hand  near  the  other  end, 
thus  bending  the  bow  until  the  other  loop  can  be  shoved  up  into  the  groove. 
Always  slip  the  loop  out  of  the  groove  when  the  bow  is  not  in  use  so  that 
it  will  not  be  permanently  bent  out  of  shape. 

The  arrow. — Cut  an  arrow  out  of  straight-grained  light  wood,  like 
cedar  or  pine,  30  inches  long  and  make  it  about  as  large  around  as  a  pencil, 
except  the  head  end,  which  for  a  distance  of  3  inches  may  be  made  f  inch 
in  diameter.  Or  the  head  end  may  be  left  the  same  size  as  the  shaft  of  the 
arrow  and  sharpened.  Then  a  bit  of  thin  brass  tubing  may  be  forced  on 
the  head  end  just  back  of  the  point  or  regular  arrow  tips  may  be  fastened  on. 

The  string  end  of  the  arrow's  shaft  is  notched  so  as  to  set  on  the  string. 
To  feather  it  split  a  chicken's  wing  or  tail  feather  in  two,  cut  the  quill 
off  J  inch  from  the  web  and  cut  the  web  off  from  the  shaft  £  inch  from  the 
other  end.  Bind  these  pieces  to  the  shaft  i  inch  from  the  string  end,  one 
on  the  top  of  the  shaft,  the  other  below  it. 

The  operation  of  the  bow  and  arrow  depends  upon  the  fact  that  the 
wood  of  the  bow  is  elastic.  When  a  body  is  distorted  by  pressure  and  then 
tends  to  resume  its  normal  shape,  exerting  a  force  in  the  attempt  to  do  so, 
this  is  known  as  elasticity.  Thus  the  bent  bow  tends  to  straighten  itself 
and  exerts  a  pressure  through  the  string  on  the  arrow  equal  to  the  force 
used  to  bend  the  bow.  When  a  rubber  ball  is  dropped  on  the  sidewalk  it 
is  distorted  by  hitting  the  hard  walk.  It  hits  back  as  it  reassumes  its 
normal  shape  and  so  throws  itself  back  into  the  air  or  bounces  from  the 
walk. 

When  muscular  energy  is  used  to  bend  the  bow  it  is  stored  in  the 
curving  wood  as  potential  energy.  When  the  string  is  released  this  potential 
or  static  energy  becomes  at  once  active  or  kinetic  and  is  imparted  to  the 
arrow,  starting  it  on  its  flight.  Thus  muscular  power  is  transformed  and 
stored  as  elasticity,  then  reappears  as  mechanical  motion,  an  illustration  of 
the  principle  of  conservation  of  energy  that  will  be  repeatedly  seen  in  the 
work  that  follows.  This  principle,  briefly  stated,  is  that  energy  cannot  be 
created  or  destroyed  but  may  be  transformed  from  one  sort  to  another. 

It  is  an  instructive  thing  to  fire  the  arrow  straight  up  in  the  air.  It 
leaves  the  bow  with  a  certain  velocity  and  momentum  which  decrease 
gradually  as  gravity  tends  to  pull  the  mounting  arrow  back  to  earth.  The 
arrow  stops  its  upward  flight  as  the  force  of  gravity  equals  the  waning 


GUIDE  IN  PHYSICAL  NATURE-STUDY 


momentum.  Then  it  begins  to  fall  slowly  at  first,  then  with  increasing 
velocity  as  gravity  continues  to  act  upon  it,  and  finally  it  strikes  the  earth 
with  sufficient  energy  to  bury  its  head  in  the  ground. 
With  what  amount  of  energy  does  it  strike? 

To  make  the  target. — 72.  Take  an  old  gunny  sack 
or  other  bag  made  of  coarsely  meshed  cloth.  Lay  it 
down  flat  on  the  floor  and  mark  one  side  of  it  with 
bull's-eye  and  concentric  circles,  using  a  grease 
pencil  or  express- marking  pencil  for  the  purpose. 
Stuff  the  bag  partly  full  of  straw  or  excelsior,  held 
in  place  by  occasional  stitches  of  darning  cotton 
through  the  bag.  Tie  the  target  up  between  two 
upright  sticks  set  in  the  ground. 

In  using  the  bow  it  is  held  vertically  in  the  left 
hand  just  below  its  center.    The  notch  in  the  end 
of  the  arrow's  shaft  is  placed  at  the  center  of  the 
§      bowstring.     The  end  of  the  shaft  is  held  between 
£      the  thumb  and  bent  forefinger  of  the  right  hand. 
The  shaft  of  the  arrow  lies  next  the  bow  on  the  base 
g      of  the  thumb  of  the  left  hand.    Draw  the  arrow 
^     back  to  its  head,  sighting  along  it  at  the  target, 
|      then  when  it  is  pointed  at  or  a  little  above  the 
%     bull's-eye  release  it  for  its  flight. 

The  bow  gun. — The  same  force,  developed  from 
^  the  elasticity  of  the  wooden  bow,  is  seen  in  several 
^  other  interesting  toys.  Long  before  the  days  of 
0-  the  modern  gun,  the  bow  gun  was  in  use  and  was 
^  called  the  cross-bow.  It  is  not  a  difficult  weapon 
to  make. 

73.  Take  a  piece  of  f-inch  stuff,  6  inches  wide 
and  3 1  feet  long.  Saw  out  the  general  form  of  a 
gun,  laying  it  out  by  the  working  plan  (Fig.  13). 
The  barrel  of  the  gun  is  left  square  at  the  outset. 
It  may  be  rounded  off  below  after  carrying  out  the 
following  directions,  if  it  is  desired.  With  a  groov- 
ing plane  or  a  gouge  cut  a  shallow  groove  along  the 
top  of  the  barrel.  Cut  a  hole  through  the  bulge 
near  the  end  of  the  barrel  to  receive  the  bow.  The 
.  bow  already  made  may  be  used,  fastening  it  at  its 
mid-point  in  this  hole  and  wedging  it  with  wooden 
wedges  to  hold  it  in  place. 


TOP,  SLING,  AND  BOW  47 

The  arrow,  some  1 8  to  20  inches  long,  should  have  a  rounded  head  so 
that  it  will  slip  along  the  groove  easily,  and  the  opposite  end  must  be  made 
wide  with  a  generous  notch  to  catch  the  string  from  the  bow  when  the 
former  is  released  in  firing  the  gun. 

The  trigger. — At  the  point  where  the  stock  of  the  gun  and  the  barrel 
meet  cut  a  slot  from  top  to  bottom  of  the  gun  in  the  midline  ij  inches 
long  and  J  inch  wide.  In  this  set  a  trigger  whose  upper  end  comes  but 
slightly  above  the  upper  face  of  the  barrel.  The  trigger  is  held  in  place 
by  a  nail  passed  through  it  and  also  through  the  sides  of  the  gun  barrel 
and  then  bent  on  one  side  to  keep  it  in  place.  Drive  a  tack  in  the  middle 
of  the  bottom  of  the  barrel  a  few  inches  in  front  of  the  trigger.  -  To  this 
attach  a  small  rubber  band  the  other  end  of  which  is  set  in  a  notch  near 
the  lower  end  of  the  trigger  to  keep  this  end  drawn  forward.  Notch  the 
top  of  the  trigger  to  receive  the  bow  string  when  the  bow  is  drawn  back. 
If  the  trigger  will  not  hold  it  add  a  stronger  rubber  band  to  the  lower  end 
of  the  trigger. 

Shooting. — Set  the  arrow  in  the  groove  on  the  upper  side  of  the  gun 
barrel.  Aim  the  gun  as  you  would  an  ordinary  piece  and  pull  the  trigger 
to  shoot  the  arrow.  The  muzzle  velocity  is,  of  course,  not  very  high. 
The  trajectory  is  therefore  a  line  that  curves  rapidly  down  toward  the 
earth's  surface  when  the  gun  is  fired  horizontally;  still,  a  little  experience 
will  make  one  fairly  expert  in  allowing  for  the  pull  of  gravity  by  sighting 
somewhat  above  the  mark,  as  one  must  do  even  with  a  high-powered  rifle 
when  firing  at  long  range. 

A  toy  pistol. — 74.  Cut  a  f-inch  square  piece  of  wood  6  inches  long 
and  fasten  another  piece  of  the  same  wood  3  inches  long  at  one  end  to  serve 
as  the  handle  or  pistol  grip,  or  the  whole  pistol  may  be  cut  out  of  a  block 
of  wood  in  the  rough  and  then  shaped  more  exactly  with  a  knife.  Rig  a 
trigger  as  in  the  cross-bow.  Fasten  two  rubber  bands  to  the  pistol,  one 
on  each  side  by  a  tack  driven  in  near  the  end  of  the  barrel  farthest  from 
the  handle.  Tie  the  ends  of  a  short  string  to  the  free  ends  of  these  rubber 
bands,  so  that  when  they  are  stretched  it  will  catch  in  the  notch  of  the 
trigger.  Just  in  front  of  the  trigger  on  the  upper  surface  of  the  barrel 
make  a  little  longitudinal  slot  with  the  end  of  the  knife.  A  piece  of  card- 
board f  inch  square  is  set  by  one  of  its  corners  in  this  slot  and  is  fired  as  the 
"bullet"  when  the  stretched  rubber  bands  are  released  by  the  trigger. 


THE  HOT-AIR  BALLOON  AND  SOME  EXPERIMENTS  TO  SHOW 

HOW  IT  WORKS 

How  to  make  a  hot-air  balloon. — 75.  Cut  sixteen  strips  of  tissue 
paper  8  inches  wide  and  5  feet  long.  These  may  be  all  of  the  same  color 
or,  if  it  is  desired  to  have  the  balloon  striped,  half  of  one  color  and  half  of 
another.  Fold  each  piece  down  the  center  so  as  to  make  a  double  strip 
4  inches  wide  and  5  feet  long.  Cut  a  strip  of  newspaper  or  heavy  brown 
paper  to  serve  as  a  pattern,  as  follows:  Cut  the  strip  5  feet  long  and  4 
inches  wide.  Mark  on  one  long  edge  a  point  at  every  foot.  At  the  first 
from  the  tip  mark  a  point  3  inches  from  this  edge  as  measured  along  a 
line  perpendicular  to  it.  At  the  second  point  mark  a  point  on  the  other 
edge  opposite  it.  At  the  third  point  mark  another  point  3  inches  from  this 
edge;  at  the  fourth,  a  point  midway  between  the  two  edges.  At  the  end 
mark  a  point  ij  inches  from  the  edge.  Beginning  at  this  last  point  draw 
a  flowing  line  to  connect  these  several  points  and  run  out  finally  to  the  corner 
aj:  the  opposite  end  from  the  start  adjacent  to  the  side  on  which  the  points 
were  spaced  a  foot  apart.  This  pointed  end  of  the  pattern  makes  the  top 
of  the  balloon.  Lay  the  pattern  on  the  folded  strips  and  the  straight  edge 
on  the  fold  and  so  cut  the  sixteen  strips. 

When  all  the  strips  are  cut  according  to  pattern  lay  one  of  the  folded 
strips  down  on  the  table,  unfold  another  strip,  and  lay  it  on  the  folded 
strip,  their  edges  parallel,  but  the  folded  strip  extending  J  inch  beyond  the 
open  strip.  Put  paste  on  the  projecting  edge  of  the  folded  strip  and  then 
turn  this  edge  back  so  as  to  paste  it  on  the  unfolded  strip.  Refold  the 
strip  that  was  opened,  open  a  third  strip  and  lay  it  on  the  refolded  one, 
and  proceed  to  paste  as  before.  In  this  way  all  of  the  strips  can  be  fastened 
together,  making  the  balloon.  Let  this  much  of  the  balloon  dry  before 
proceeding  with  the  next  step. 

The  strips  cannot  be  made  to  meet  exactly  at  their  upper  sharp  ends, 
so  that  there  will  be  a  small  hole  in  the  top  of  the  balloon.  Cut  two  circular 
patches  of  paper  8  or  10  inches  in  diameter,  and  paste  these  on,  one  inside 
and  one  outside  of  the  hole  so  as  to  cover  the  hole. 

Bend  a  thin  piece  of  bamboo  J  inch  wide  so  as  to  make  a  hoop  just 
large  enough  to  fit  inside  the  mouth  of  the  balloon.  Fasten  the  ends  of 
the  strip  by  binding  with  string.  Fasten  the  hoop  in  by  folding  the  tissue 
paper  up  over  it  and  pasting  it  on  the  inside  of  the  balloon.  Run  two  light 
iron  wires  across  the  mouth  of  the  balloon,  fastening  their  ends  to  the  bam- 

48 


THE  HOT-AIR  BALLOON  AND  SOME  EXPERIMENTS  49 

boo  hoop  and  placing  them  so  that  they  cross  each  other  at  right  angles  at 
the  center  of  the  hoop. 

Pass  the  ends  of  a  loop  of  string  through  the  center  of  the  circular 
patch  on  the  top  of  the  balloon  and  fasten  these  ends  by  pasting  paper 
over  them  on  the  inside  of  the  balloon.  This  loop  will  serve  to  hang  up 
the  balloon,  and  to  hold  the  balloon  when  it  is  being  inflated  with  hot  air. 
It  is  well  now  to  hang  the  balloon  up  after  the  fastenings  of  the  loop  are 
dried  and  examine  it  to  see  that  there  are  no  holes,  covering  them  with 
pieces  of  paper  pasted  on  if  any  are  found. 

Bend  a  piece  of  wire  6  inches  long  into  the  shape  indicated  in  the  diagram 
(Fig.  14) ;  on  the  center  of  this  wind  a  ball  of  lamp  wick  or  cotton  batting. 
This  to  be  saturated  with  alcohol,  slipped  on  one  of  the  cross-wires  at  the 
mouth  of  the  balloon,  and  lit  just  before  the  balloon  is  sent  up  so  as 
keep  the  air  inside  the  balloon  hot.  To  prevent  the  flame  setting  the  balloon 
afire  make  a  cylinder  of  asbestos  paper  6  inches  long 
and  3  inches  in  diameter.  Cut  four  slots  2  inches 
long  in  one  end  of  this  so  that  this  chimney  will  set 
down  on  the  cross-wires  around  the  ball  of  wicking. 
Inflating  it. — The  balloon  must  be  filled  with  hot 
air  before  it  is  sent  up.  To  do  this  take  a  length  of 
stovepipe,  cut  a  piece  out  of  one  end  and  set  this 
end  down  in  the  ground,  forcing  it  into  the  ground 
for  some  distance.  A  wood  fire  is  then  built  in  the 
stovepipe,  the  hole  at  the  bottom  serving  as  a  draft  ^  ^  —Bent  wire 

to  let   in  the  air.     When  the  fire  has  died  down      for  hanging  wicking  to 
some,  so  that  the  flames  are  no  longer  coming  from      balloon  frame, 
the  top  of  the  pipe,  hold  the  mouth  of  the  balloon 

over  the  top  of  the  pipe.  It  is  best  to  place  a  stick  through  the  loop 
at  the  top  of  the  balloon,  one  person  holding  this  while  a  second  person 
holds  the  mouth  of  the  balloon.  Pull  out  the  sides  of  the  balloon  to 
straighten  out  folds  so  that  it  will  inflate  to  its  capacity.  When  the 
balloon  is  well  distended  with  hot  air,  take  it  away  from  over  the  stove- 
pipe, put  on  the  ball  of  wicking  saturated  with  alcohol  and  the  asbestos 
chimney,  light  the  alcohol.  Remove  the  stick  now  from  the  loop.  Let 
the  person  who  is  holding  the  mouth  continue  to  hold  it  until  the  balloon 
begins  to  tug  a  bit,  then  let  go  and  it  will  rise  and  probably  drift  out  of  sight. 

It  is  well  not  to  try  to  send  the  balloon  up  on  a  windy  day.  Fill  it  in  a 
sheltered  position,  but  select  a  place  where  it  will  not  get  tangled  among 
tree  branches,  telephone  wires,  or  blow  against  a  building  as  it  rises. 

The  remainder  of  this  chapter  will  consist  of  experiments  to  make  clear 
why  the  balloon  rises.  Incidentally  some  other  things  will  be  explained. 


50  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Water  seeks  its  own  level. — 76.  Slip  a  ij-foot  length  of  rubber  tubing 
on  the  end  of  a  good-sized  funnel  and  put  a  smaller  funnel  on  the  other 
end  of  the  rubber  tubing.  Hold  the  two  funnels  in  the  left  hand,  and 
pour  water  into  one  of  them  until  it  rises  into  the  other.  Take  one  funnel 
in  one  hand  and  one  in  the  other  and  vary  their  relative  levels.  It  will  be 
noted  that  the  level  of  the  water  is  the  same  in  the  tube  even  when  the 
large  funnel  is  quite  well  filled,  thus  having  a  large  water  surface,  while 
the  level  of  the  water  in  the  small  funnel  may  be  only  part  way  up  the 
stem  of  the  funnel. 

The  fountain. — 77.  Substitute  for  the  small  funnel  a  piece  of  glass 
tubing,  drawn  out  into  a  fine  point.  To  do  this  cut  an  8-inch  length  of 
glass  tubing  as  follows: 

78.  To  cut  glass  tubing  make  a  scratch  on  the  glass  with  a  triangular 
file  at  the  point  at  which  you  want  it  to  break.    Hold  it  in  the  hands,  with 
the  thumbs,  nail  to  nail,  opposite  the  scratch,  the  fingers  on  the  scratched 
side  of  the  tube.    Press  up  with  the  thumbs  and  down  with  the  fingers, 
when  the  tubing  will  easily  break  straight  across. 

79.  Hold  the  glass  tube  by  its  ends  and  let  the  middle  of  it  heat  in 
the  gas  flame  or  the  flame  of  the  alcohol  lamp,  turning  it  slowly  until  it 
is  red  hot  and  bends  easily.    Then  quickly  pull  the  ends  apart.    Break  off 
the  tip  when  cool.    Hold  the  large  funnel  and  the  tube  in  the  left  hand 
and  fill  the  apparatus  with  water.    Cover  the  tip  of  the  tube  with  the 
finger  and  lower  it,  the  tip  pointing  up.    When   the  finger  is  removed 
the  water  plays  like  a  fountain,  rising  approximately  to  the  level  of  the 
water  in  the  funnel.     Why  not  to  the  level?    The  principle  illustrates  the 
method  by  means   of   which   water   is   conducted   into  houses   through 
pipes,  when  the  water  gets  its  pressure  from  some  reservoir  that  stands  at 
an  elevation. 

Water  pressure. — 80.  With  a  nail  set  or  large  wire  spike,  make  a 
round  hole  in  the  top,  one  side,  and  the  bottom  of  a  tin  can  with  a  very 
tight  cover.  Put  small  rubber  corks,  each  with  a  hole,  into  these  openings. 
Pass  a  small  funnel  through  the  hole  of  the  cork  in  the  top  of  the  can,  a 
glass  tube  with  a  right-angled  bend  through  the  hole  in  the  side  of  the  can, 
and  one  with  two  right-angled  bends  both  on  the  same  side  of  the  straight 
portion,  through  the  hole  at  the  bottom  of  the  can  (see  Fig.  15).  To 
bend  the  glass  tubing  proceed  as  follows: 

81.  Heat  the  tubing,  at  the  point  where  the  bend  is  to  be  made,  in  the 
flame  of  an  alcohol  lamp  or  a  Bunsen  gas  burner.  Hold  it  up  near  the  tip 
of  the  flame  and  turn  it  slowly  so  that  it  will  heat  on  all  sides.  Glass  is 
a  poor  heat  conductor,  so  that  it  may  be  held  in  the  fingers  while  this  is 
being  done.  Soon  the  glass  will  soften  so  that  it  can  be  slowly  bent.  If  the 


THE  HOT-AIR  BALLOON  AND  SOME  EXPERIMENTS  51 

bending  is  done  rapidly  the  hole  through  the  tube  is  likely  to  be  closed, 
and  we  want  it  open. 

Seal  the  cover  on  the  can  by  putting  on  a  strip  of  surgeon's  adhesive 
tape,  which  can  be  bought  at  the  drug  store.  Pour  water  into  the  funnel, 
filling  the  can,  and  continue  to  pour  it  in  until  the  water  stands  in  the  funnel 
2  or  3  inches  above  the  top  of  the  can.  Tilt  and  jar  the  can  to  get  out  all 
air  bubbles.  Note  the  water  level  in  the  tubes  and  observe  in  what  direc- 
tion the  pressure  must  be  exerted  in  the  can  to  maintain  it  at  this  level. 
What  determines  with  what  force  the  water  strikes  the 
paddles  in  project  64? 

Pumps. — In  any  city  water-supply  system  in  which 
there  is  no  large  reservoir,  the  supply  pipes  are  kept 
filled  and  the  pressure  is  maintained  by  a  force  pump; 
and  in  the  ordinary  well  the  water  is  obtained  by  a 
lift  pump. 

82.  The  lift  pump  is  made  readily  as  follows:  Take 
a  length  of  good-sized  glass  tubing  12  inches  long,  a 

parafinned  mailing- tube,  or  a  piece  of  bamboo.     Cut  a         FlG- 15.— Diagram 

piece  of  wood   15   inches  long  and  about  as   large    of  can  with  tubes  to 

illustrate  water  pres- 
around  as  a  lead  pencil,  for  the  plunger  handle.     At     sure 

one  end  of  this  fit  a  slice  of  cork  for  a  plunger  and 
fasten  it  securely.  The  cork  should  fit  the  tube  snugly.  Punch  a  hole 
through  the  cork  and  then  with  a  small  tack  fasten  a  flap  of  leather  so 
that  it  will  cover  the  hole  on  the  handle  side,  the  tack  being  placed  at 
one  side  of  the  hole.  The  cork  should  be  free  to  slip  up  and  down 
rather  tightly  in  the  tube  when  worked  by  the  lift  handle.  Put  a 
cork  in  the  lower  end  of  the  tube,  having  first  made  a  hole  in  it  and 
covered  the  hole  with  a  leather  flap  held  by  a  tack,  the  flap  being  on  the 
inner  face  of  the  cork.  Put  this  corked  end  of  the  tube  in  the  water  and 
work  the  plunger  back  and  forth.  If  properly  constructed  the  water  rises 
in  the  tube  and  is  pumped  out  at  the  top.  A  tube  made  of  rolled 
paper  may  be  set  in  the  mailing  tube  or  bamboo  with  glue,  to  serve  as 
a  spout. 

The  force  which  impels  the  water  up  the  tube  is  the  pressure  of  the  air. 

83.  Take  a  piece  of  glass  tubing,  fill  it  with  water  by  simply  laying  it 
down  in  a  pan  of  water;  put  the  finger  over  one  end  of  the  tube  and  raise 
this  out  of  the  water,  leaving  the  other  end  in  the  water.    The  water  re- 
mains up  in  the  tube  but  drops  the  minute  the  finger  is  taken  off  the  open 
end.     Why? 

The  leather  sucker. — 84.  Cut  a  circular  piece  of  leather   (as  from  the 
top  of  an  old  boot  or  shoe)  2  inches  in  diameter.    With  a  heavy  needle 


52  GUIDE  IN  PHYSICAL  NATURE-STUDY 

pass  a  2-foot  length  of  string  through  its  center.  Tie  a  knot  in  one  end 
of  the  string  and  draw  the  knot  up  to  the  leather.  Soak  the  leather  in  water 
for  some  time.  Apply  the  leather,  knot  side  down,  closely  to  a  smooth 
surface,  like  that  of  glass,  and  pull  on  the  string.  The  disk  should  adhere 
vigorously,  resisting  quite  a  strong  pull  before  it  detaches  from  the  surface. 
Why? 

An  experiment. — Try  this  experiment  and  explain  what  happens: 

85.  Pass  a  i -foot  length  of  glass  tubing  through  a  rubber  cork  that 
will  fit  into  the  mouth  of  a  flask.  Draw  out  the  end  of  the  tube  projecting 
from  the  small  end  of  the  cork  in  the  flame,  so  that  it  is  a  fine  tube.  Break 
off  the  excess  of  glass  tubing.  Put  a  tablespoonful  of  ;water  into  the  flask. 
Let  the  water  in  the  flask  boil  for  a  minute,  then  insert  the  cork.  Handling 
the  flask  with  tongs,  turn  it  upside  down  and  stick  the  free  end  of  the  glass 
tube  into  a  vessel  full  of  cold  water. 

To  make  a  squirt  gun. — 86.  Fit  a  cork  into  one  end  of  a  good-sized 
glass  tube  or  length  of  bamboo,  but  before  inserting  it  file  or  cut  a  groove 
on  one  side.  Make  a  plunger,  as  was  done  for  the  pump,  except  that  there 
will  be  no  valve  in  this.  Put  the  head  of  the  plunger  into  the  free  end  of 
the  tube  or  length  of  bamboo,  drive  it  down  nearly  to  the  cork,  put  the 
corked  end  under  water,  draw  the  plunger  back  slowly,  lift  the  corked 
end  above  the  water,  and  drive  the  plunger  rapidly  down.  This  squirt 
gun  illustrates  the  principle  of  the  force  pump. 

The  force  pump. — As  the  stream  of  water  comes  from  the  force  pump 
into  the  faucets  in  the  house,  or  from  the  hose  nozzle  connected  to  the 
fire  engine,  the  stream  is  a  steady  stream  and  not  a  succession  of  spurts. 
This  change  is  brought  about  by  the  addition  of  an  air  chamber,  which 
has  an  inlet  and  an  outlet.  The  water  coming  in,  in  a  succession  of  spurts, 
crowds  up  against  the  cushion  of  elastic  air,  the  pressure  of  which  sends 
the  water  out  in  a  steady  stream.  87.  Replace  the  cork  in  the  squirt 
gun  with  one  having  two  holes,  one  for  intake,  one  for  outlet.  Put  short 
lengths  of  glass  tubing  in  each  so  that  the  ends  are  flush  with  the  small 
end  of  the  cork.  Attach  a  leather  valve  over  the  intake  tube  so  that  it 
will  let  water  in  but  not  out.  Attach  a  rubber  tube  to  the  intake  pipe 
and  let  its  free  end  set  in  a  glass  of  water.  Fit  a  cork  with  two  holes  into 
a  4-ounce  wide-mouthed  bottle.  Put  short  lengths  of  glass  tubing  into  the 
cork,  their  ends  flush  with  the  inner  end  of  the  cork.  Put  a  valve  over 
one  so  that  it  will  let  water  in.  Connect  this  one  by  a  short  length  of 
rubber  tubing  to  the  outlet  of  the  squirt  gun,  now  to  be  used  as  a  force 
pump.  Connect  a  short  rubber  tube  to  the  outlet  of  the  small  bottle  and 
put  a  pipette  glass  into  the  other  end  of  this  rubber  tube.  Then  operate 
the  pump  and  a  steady  stream  will  issue  from  the  pipette  "nozzle." 


THE  HOT-AIR  BALLOON  AND  SOME  EXPERIMENTS  53 

Why  lead  sinks  but  cork  floats. — 88.  Cut  a  piece  of  plasticine  or 
putty  into  the  shape  of  a  rectangular  solid  i  by  i  by  5  centimeters,  or 
hammer  a  piece  of  lead  into  this  shape.  Tie  a  string  about  it  so  that  it 
hangs  with  its  long  axis  vertical.  Then  let  it  down  into  a  glass  cylinder 
graduated  to  100  c.c.  or  more  tha't  is  all  filled  with  water  up  to  the  50  c.c. 
mark.  When  the  block  of  plasticine  is  under  water  what  is  the  level  of 

the  water  in  the  cylinder?    The  water  has   risen c.c. 

What  is  the  volume  of  the  plasticine  block? c.c.    A  solid 

body  then  when  immersed  in  water  displaces volume 

of  water. 

89.  Tie  a  small  glass  cylinder  or  bottle  to  a  spring  scale  or  set  it  on 
a  balance.    Note  how  much  it  weighs  in  grams.    Pour  into  it  10  c.c.  of 

water.    Weigh  again.    The  water  weighs  how  much? grams. 

One  cubic  centimeter  of  water  weighs grams.     Fasten  the 

string  to  which  the  plasticine  block  is  tied  to  the  hook  of  the  spring  scale. 

What  does  the  block  weigh? Let  it  down  into  the  water. 

When  it  is  in  water  it  weighs grams.    When  immersed  in  water 

it  loses grams  of  its  air  weight.    But  this  is  the  weight  of  the 

water Since  water  pressure  at 

a  given  level  is  equal  in  all  directions,  the  pressure  on  the  opposite  vertical 
faces  of  the  quadrangular  block  must  be  equal,  for  they  are  identical  in 
area  and  in  position  point  for  point.    But  the  upward  pressure  on  the  bottom 
of  the  block  will  not  be  equal  to  the  downward  pressure  on  the  top  of  the 

block,  though  their  areas  are  equal,  but  it  will  be by  the 

weight  of  a  column  of  water,  which  is  the  size  of  block  sustained  by  the 
scales. 

90.  Cut  a  cube  2  centimeters  on  each  edge  from  a  good-sized  cork  or  block 
of  wood  and  weigh  it.    Then  let  it  float  in  water  and  mark  the  level  to  which 
it  sinks  in  the  water.    Measure  the  depth  to  which  it  sinks  and  calculate  (or 
measure)  the  volume  of  water  it  displaces  when  floating.    The  weight  of  this 

water the  weight  of  the  cork  or  in  other  words  the 

upward  pressure  on  the  lower  surface  of  the  cork  cube  is 

than  that  on  the  upper  surface  by  an  amount 

Why  does  a  boat  float  even  when  made  of  iron,  which  so  readily  sinks? 
How  much  of  a  load  can  you  put  into  a  boat  without  danger  of  its  sinking? 
Archimedes'  problem. — 91.  Squeeze  the  block  of  plasticine  used  above 
out  of  shape  so  that  it  is  no  longer  rectangular  but  is  irregular  in  shape. 
Again  immerse  it  in  the  50  c.c.  of  water  in  the  graduate.  How  much 
water  does  it  displace?  How  could  you  find  the  volume  of  a  key?  Find 
out  how  many  times  heavier  than  water  it  is.  Archimedes  was  once  given 


54  GUIDE  IN  PHYSICAL  NATURE-STUDY 

a  problem  to  work  out  on  an  examination  and  if  he  flunked  he  was  told 
by  the  king  that  he  would  lose  his  head!  Some  motivation!  What  was 
his  problem  and  how  did  he  solve  it?  If  you  wear  a  plain  gold  ring  can  you 
tell  if  it  is  pure  gold?  (First  find  out  from  a  book  how  many  times  pure 
gold  is  heavier  than  water.) 

Why  the  balloon  rises. — The  hot-air  balloon  goes  up  for  the  same 
reason  that  the  cork  floats.  It  floats  in  air.  The  fluid  in  which  it  is  immersed 
is  a  gas  instead  of  a  liquid.  It  will  be  well  to  have  experience  with  some 
characteristic  gases. 

To  make  chlorine  gas. — 92.  Fit  a  cork  into  the  mouth  of  a  good-sized 
test  tube.  With  a  rat-tail  file  punch  and  file  out  a  hole  through  the  center 
of  the  cork  so  that  it  will  take  tightly  one  end  of  an  8-inch  length  of  glass 
tubing.  (To  cut  glass  tubing  see  p.  50.) 

Bend  the  tubing  into  the  shape  of  a  hook,  making  a  bend  about  two 
inches  from  one  end  (see  p.  50). 

Put  the  short  end  of  the  tube  through  the  cork.  Put  about  a  teaspoon- 
ful  of  strong  chlorhydric  acid  into  the  test  tube  and  mix  with  it  half  as 
much  granular  manganese  dioxide,  or  you  may  use  a  heaping  teaspoonful  of 
chloride  of  lime  in  place  of  these.  Then  put  the  cork  with  its  tube  into  the 
mouth  of  the  test  tube  and  hang  the  bend  of  the  tube  over  the  ring  of  a 
ring  stand  or  hold  the  test  tube  with  a  test-tube  holder.  Apply  the  flame 
of  the  alcohol  lamp  or  Bunsen  burner  to  the  lower  end  of  the  test  tube. 
As  the  material  heats  the  yellowish  chlorine  gas  is  given  off  and  passes 
out  through  the  tube.  Put  a  bottle  under  the  mouth  of  the  tube.  This 
gas  is  heavier  than  air  and  sinks  to  the  bottom  of  the  bottle,  forcing  the 
air  out.  Be  careful  not  to  inhale  any  quantity  of  the  gas  for  it  is  irritating 
and  tends  to  choke  you.  It  is  this  chlorine  gas  that  was  used  in  the  early 
"gas  attacks"  in  the  war.  This  gas  is  chosen  for  our  experiment  because 
it  is  colored  and  can  so  readily  be  seen. 

To  make  hydrogen. — 93.  Use  the  same  sort  of  a  test-tube  generator 
as  was  used  above  for  the  chlorine,  but  run  the  free  end  of  the  glass  tube 
through  a  cork  that  fits  a  wide-mouthed  bottle  of  about  8-ounce  capacity 
so  that  the  end  of  the  tube  will  be  close  to  the  bottom  of  the  bottle.  Cut  a 
second  hole  in  the  cork  of  this  large-mouthed  bottle  and  run  through  it  a 
3-inch  length  of  glass  tubing.  Put  a  short  length  of  rubber  tubing  on  this 
glass  tube  and  the  other  end  of  it  on  the  stem  of  an  ordinary  clay  pipe. 
Fill  the  wide-mouthed  bottle  about  half  full  of  water.  Fill  the  test  tube 
one-sixth  full  of  granulated  zinc.  Cover  this  with  water  and  then  pour 
enough  chlorhydric  acid  in  so  that  the  hydrogen  gas  will  begin  to  bubble  up 
freely.  The  hydrogen  is  colorless  and  odorless.  .If  the  test  tube  is  fitted 
to  the  cork  that  carries  the  delivery  tube  the  hydrogen  will  flow  through 


THE  HOT-AIR  BALLOON  AND  SOME  EXPERIMENTS  55 

the  latter  into  the  water,  will  bubble  up  through  the  water,  and  will  escape 
out  of  the  wide-mouthed  bottle  through  the  rubber  tube  and  the  clay 
pipe.  Have  ready  some  soap  suds,  the  sort  that  you  would  use  to  blow 
bubbles.  Dip  the  mouth  of  the  pipe  in  the  suds,  then  lift  it  so  that  the 
bubbles  may  form  at  the  mouth  of  the  pipe.  Shake  the  bubble  off  when 
it  is  fairly  large.  If  it  does  not  shake  from  the  mouth  of  the  pipe,  remove 
the  pipe,  blow  the  bubble  on  the  end  of  the  rubber  tube.  The  result  will 
tell  you  whether  hydrogen  is  lighter  or  heavier  than  air.  It  is  advisible 
to  keep  flame  away  from  the  neighborhood  of  this  experiment  as  hydrogen 
forms  an  explosive  mixture  with  air. 

Heat  expands  things. — We  will  need  to  make  clear  why  the  hot  air 
on  the  inside  of  the  balloon  is  lighter  than  the  surrounding  air  to  under- 
stand why  the  balloon  goes  up.  94.  Cut  a  1 2-inch  length  of  small  glass 
tubing  and  run  it  through  a  perforated  cork  that  just  fits  the  mouth  of 
a  small  flask.  Fill  the  flask  one-fourth  full  of  water  and  put  the  cork  in  so 
that  the  water  will  rise  a  bit  in  the  tube.  Hold  the  flask  in  the  hand  or 
heat  it  over  the  flame.  What  happens  and  what  does  this  show?  What 
common  instrument  about  the  home  or  in  the  schoolroom  illustrates 
the  same  thing?  You  may  demonstrate  this  in  another  interesting  way. 
95.  Take  a  good-sized  iron  bolt  that  fits  a  nut.  Heat  the  bolt  and  then  try 
to  get  the  nut  on.  Can  you  tell  how  iron  tires  are  put  on  wooden  wheels  so 
that  they  will  fir  tightly?  Now  can  you  tell  why  the  air  in  the  balloon 
was  heated  before  the  balloon  was  released?  And  why  heating  the  air 
made  that  inside  of  the  balloon  lighter  than  an  equal  volume  outside  of 
the  balloon? 


SOME  COMMON  APPLIANCES  THAT  OPERATE  BY  HEAT 

Air  currents. — 96.  Set  a  lighted  candle  or  a  Bunsen  burner  on  the 
table  and  then  put  a  lamp  chimney  over  it.  Support  the  chimney  on 
blocks  of  wood  or  the  ring  of  a  ring  stand.  Bring  a  smoking  joss  stick 
or  a  tightly  rolled  wisp  of  paper  that  is  smoking  near  the  base  of  the 
chimney.  Notice  the  direction  taken  by  the  smoke.  Why  does  it  move 
thus?  Draw  a  diagram  of  this  apparatus,  showing  how  the  smoke  moves. 
Can  you  see  how  this  principle  applies  to  the  heating  of  a  house  with  a 
hot-air  furnace  ?  Suppose  the  region  where  you  live  were  very  hot,  the  sun 
heating  the  land  intensely.  Suppose,  further,  that  some  nearby  region 
were  protected  from  the  sun's  rays  by  clouds  so  that  the  area  was  not  as 
hot.  What  would  happen? 

Making  ice. — 97.  Put  a  drop  of  chloroform  or  ether  on  the  back  of 
your  hand  with  a  medicine  dropper.  What  becomes  of  it  immediately? 
How  does  the  spot  on  your  hand  feel?  98.  Put  some  water  in  a  small  tin 
pan  or  evaparating  dish  and  heat  it.  Keep  the  bulb  of  a  thermometer  that 
registers  at  least  212°  F.  in  the  water  as  it  heats.  When  the  water  boils 
what  does  the  thermometer  register?  As  you  apply  more  heat  does  the 
temperature  of  the  water  continue  to  rise?  Why? 

99.  Take  a  3-inch  square  piece  of  clean  sheet  zinc.    Lay  a  piece  of  sheet 
copper  on  a  drop  of  water  placed  on  the  zinc.     Drop  ether  or  chloroform 
on  the  copper  and  blow  on  it.     In  a  few  moments  the  water  between  the 
two  is  frozen.    Why? 

100.  Put  a  piece  of  ice  in  a  tin  pan  or  evaporating  dish  and  apply  heat 
to  it.     As  it  melts  put  the  thermometer  bulb  in  the  water  that  forms. 
Note  what  the  thermometer  registers.    Continue  to  heat.    Does  the  tem- 
perature of  the  water  rise?    Why?     Could  you  determine  where  the  32°- 
point  and  the  2i2°-point  should  go  on  a  thermometer  if  you  were  making 
one? 

To  make  a  cloud. — 101.  Fit  a  rubber  cork  with  two  holes  in  it  to  the 
mouth  of  a  large  flask  of  at  least  2 -liter  capacity  or  to  a  large  bottle.  Insert 
one  long  straight  glass  tube  through  the  cork  so  that  it  will  run  within  an 
inch  of  the  bottom  of  the  flask  and  project  above  the  cork  i  inch,  and  a 
short  one  through  the  other  hole  so  that  it  will  project  i  inch  on  both  sides 
of  the  cork.  Equip  another  flask  or  bottle  of  the  same  size  in  the  same  way. 
Connect  the  two  flasks  with  a  3-foot  length  of  rubber  tubing,  the  ends  of 
which  slip  on  the  protruding  ends  of  the  short  tubes  in  the  two  bottles. 

56 


SOME  COMMON  APPLIANCES  OPERATED  BY  HEAT  57 

Put  a  compression  clamp  on  this  tube  and  close  it.  Slip  short  lengths  of 
rubber  tubing  to  the  outer  ends  of  the  two  long  tubes  and  have  compression 
clamps  ready  to  close  these. 

Fill  one  flask  five-sixths  full  of  water,  and  after  putting  the  cork  in 
tightly  set  it  mouth  down  in  a  large  ring  on  a  stand  placed  near  the  edge  of 
a  table  in  strong  light.  We  will  designate  this  flask  A  the  other  one,  B~ 
Fill  B  one-third  full  of  water,  cork  tightly,  and  hold  it  mouth  down  in  the 
left  hand  at  about  the  level  of  A .  Hold  a  smoking  joss  stick  or  wisp  of 
paper  near  the  free  end  of  the  long  glass  tube  of  flask  A  and  let  a  second 
person  open  the  compression  clamp.  Water  runs  from  A  to  B  and  at  the 
same  time  smoke  is  drawn  into  the  space  above  the  water  in  A .  Put  the 
compression  clamps  on  the  short  rubber  tubes  on  the  flasks  and  close  them, 
removing  the  clamp  on  the  long  connecting  tube. 

Raise  flask  B  as  far  as  the  rubber  tube  will  permit.  The  pressure  on 
the  air  and  its  contained  water  vapor  in  A  is  increased.  Lower  B  as  far 
as  possible  and  look  for  a  "cloud"  as  a  slight  haze  over  the  water  in  flask  A. 
The  smoke  was  drawn  into  A  so  that  its  particles  might  act  as  condensa- 
tion nuclei  for  the  vapor.  Do  you  see  why  decreasing  the  pressure  on  the 
air  and  vapor  in  A  produces  condensation  to  form  the  cloud? 

Why  the  ice-cream  freezer  freezes. — 102.  Chop  about  a  pound  of  ice 
up  into  pieces  as  big  as  peas.  Mix  some  coarse  salt  with  this  and  put 
the  mixture  in  a  tumbler.  Set  the  tumbler  on  a  few  drops  of  water  on  a 
piece  of  glass.  Put  a  thermometer  bulb  in  the  salt  and  ice  mixture.  Note 
at  intervals  what  it  registers.  Probably  the  tumbler  will  freeze  to  the 
glass  on  which  it  sets  in  a  short  time.  What  happens  gradually  to  the  ice? 
When  salt  stands  in  the  salt  shaker  at  home  it  cakes  and  is  hard  to  get  out. 
Does  this  happen  most  quickly  in  moist  or  dry  weather?  Why?  Pile  a 
half-teaspoonful  of  salt  on  a  piece  of  ice.  What  happens?  What  did  we 
find  above  was  needed  to  make  ice  melt?  Now  can  you  tell  why  the  cream 
freezes  in  the  freezer? 

Why  do  you  have  a  wooden  or  woven  wire  handle  on  the  poker 
or  stove  lifter?  103.  Cut  a  piece  of  No.  18  copper  wire  8  inches  long 
and  one  of  iron  wire  of  the  same  size  and  the  same  length.  Twist  them 
together  at  one  end  so  as  to  form  a  V.  Fix  a  little  ball  of  paraffin  or  bees- 
wax on  each  wire  halfway  from  the  point  of  the  V  to  the  end.  Hold  the 
point  of  the  V  in  the  flame,  the  arms  horizontal,  with  the  wax  balls  down. 
Continue  heating  until  both  balls  fall  off.  What  do  you  learn?  104.  Try 
the  same  experiment  with  two  similar  wires  of  copper  or  iron,  one  coarse 
and  one  fine.  Hold  a  4-inch  length  of  iron  rod  in  the  hand  and  an  equal 
length  of  glass  rod,  of  the  same  size  in  the  other  hand.  Hold  the  other  ends 
together  in  the  flame  until  one  or  the  other  is  distinctly  hot  at  the  end 


58  GUIDE  IN  PHYSICAL  NATURE-STUDY 

that  you  are  "holding.  What  do  you  learn?  Is  dry  wood  a  good  or  a  poor 
conductor  of  heat? 

Why  put  a  storm  sash  on  a  window? — 105.  Hold  the  bulb  of  a  thermom- 
eter 6  inches  to  one  side  of  the  flame  of  the  Bunsen  burner  or  the  stove 
for  a  minute  and  see  what  rise  the  mercury  makes  in  that  time.  Take 
two  old  photograph  plates  that  have  been  cleaned,  or  similar  pieces  of 
glass,  and  tie  them  together  with  a  couple  of  strips  of  wood  between  to 
separate  them  J  inch.  Interpose  these  glass  plates,  held  vertically  be- 
tween the  flame  and  the  bulb  of  the  thermometer  again  held  6  inches 
to  one  side  of  the  flame.  .How  much  does  the  mercury  rise  now  in  one 
minute.  106.  Light  a  candle  and  with  a  concave  mirror  focus  the  light 
from  the  flame  on  the  bulb  of  a  thermometer.  Is  the  heat  focused  there 

too?  Evidently  the  surface  of  a  mirror heat  as 

well  as  light.  107.  Interpose  an  electric  light  bulb  between  the  flame  and 
the  bulb  of  the  thermometer  held  6  inches  to  one  side  of  the  flame.  What 
is  the  rise  of  the  mercury  now  in  one  minute?  Is  there  any  air  inside  the 
bulb?  108.  To  find  out,  break  the  tip  of  the  bulb  off  while  holding  it 
under  water.  This  can  readily  be  done  if  a  scratch  is  filed  part  way  across 
the  base  of  the  tip  and  then  the  tip  is  twisted  off  with  pliers. 

The  icy-hot  bottle. — 109.  Examine  a  thermos  bottle,  a  broken  one  if 
possible.  Note  the  space  between  the  inside  and  outside  walls  of  the  glass 
jacket.  This  is  a  more  or  less  complete  vacuum  in  good  makes  of  bottles. 
Can  you  tell  why?  Why  are  the  glass  walls  of  the  jacket  mirrored? 

To  make  a  tireless  cooker. — no.  Procure  one  or  two  aluminum  or 
tin  pails,  the  size  you  want  to  use  in  the  cooker,  say,  four  quarts.  Take 
a  wooden  box  in  which  the  pail  or  pails  may  be  set  and  leave  6  inches 
between  them  and  as  much  space  between  the  pail  and  the  outside  of  the 
box  all  around.  Cut  a  if -inch  strip  from  the  top  edge  of  the  box  and  fasten 
this  with  brads  or  small  nails  to  the  cover  as  a  rim  all  around  it.  Line  the 
bottom  of  the  box  with  asbestos  board.  Put  J-inch  strips  across 
each  end  of  the  bottom.  Set  on  these  a  false  bottom  of  J-inch  stuff, 
covered  both  sides  with  asbestos  board.  Set  the  pails  6  inches  apart  on  a 
|-inch  board  that  is  as  long  as  the  box  is  inside  and  with  a  pencil  draw  a 
mark  on  the  board  around  the  bottom  of  the  pail,  thus  making  a  circle 
about  f-inch  larger  than  the  pail  all  around.  Tack  cleats  across  the  ends 
of  the  box  i  inch  below  the  upper  edge,  and  on  these  lay  the  board  out  of 
which  the  holes  have  been  cut.  Fit  additional  boards  on  either  side  of  it 
to  make  an  inside  cover,  the  holes  about  in  the  midline  lengthwise.  Lay  the 
circular  boards  on  the  bottom  of  the  box,  their  centers  directly  under  the 
centers  of  the  holes,  and  fasten  them  in  place.  Line  the  box  with  asbestos 
board,  covering  also  the  bottom  of  the  cover  except  the  circular 


SOME  COMMON  APPLIANCES  OPERATED  BY  HEAT  59 

holes.  Cut  a  strip  of  asbestos  board  long  enough  and  wide  enough  to  make 
a  cylinder  of  double  thickness  that  will  fit  about  the  circular  block  on  the 
bottom  of  the  box  and  extend  up  through  the  circular  holes  in  the  inside 
cover  flush  with  its  top.  Tack  these  onto  the  circular  boards.  Fill  the 
space  between  them  and  the  asbestos-lined  sides  of  the  box  with  chopped 
straw  or  excelsior.  Put  the  inside  cover  in  place  and  tack  the  asbestos 
cylinders  to  the  inside  of  the  holes.  Line  the  cover  of  the  box  with  asbestos 
board  and  tack  a  piece  as  large  as  the  cover  to  the  bottom  of  the  rim  all 
around  so  that  there  will  be  an  air  space  between  it  and  the  asbestos  lining 
of  the  cover.  Hinge  the  cover  to  the  box.  Set  the  pails  in  the  asbestos 
cylinders  and  the  cooker  is  ready  to  use.  Castors  may  be  put  on  it  to 
facilitate  moving  it  about.  Why  are  so  many  air  spaces  provided  in  the 
construction?  Why  pack  it  with  chopped  straw?  Would  straw  be  better 
than  excelsior  or  the  reverse,  and  why?  Which  would  be  the  warmer, 
tightly  woven  or  loosely  woven  clothing,  weight  for  weight?  Why  are 
bed  quilts  lined  with  a  cotton  batting?  Would  wool  batting  be  any  better? 
Why? 

Heating  the  house. — When  holding  the  thermometer  bulb  beside  the 
flame  in  the  experiment  above,  the  heat  went  to  the  bulb  directly  through 
the  air,  and  such  a  process  is  called  heating  by  radiation.  When  you  held 
the  glass  and  iron  rods  in  the  flame,  the  heat  came  to  your  fingers  by  con- 
duction. In  the  experiment  with  the  flame  in  the  lamp  chimney  we  have 
seen  how  the  heated  air  rises  and  the  cooler  air  comes  in  to  take  its.  place, 
as  indicated  by  the  movement  of  the  smoke.  In  holding  your  hand  above 
the  chimney  it  is  warmed  by  the  heat  conducted  to  it  as  the  particles  of 
air  bump  against  it.  But  the  moving  air  currents  are  called  "convection 
currents,"  and  the  hand  is  so  warmed  by  convection  and  conduction.  These 
convection  currents  can  easily  be  rendered  visible  as  water  is  heated. 
in.  Set  a  good-sized  beaker  of  cold  water  on  a  ring  stand  or  other  support 
and  put  the  flame  of  the  alcohol  lamp  below  it  so  that  the  tip  of  the  flame 
is  below  the  middle  of  the  beaker's  bottom.  Dust  in  some  finely  powdered 
carmine  or  some  starch  and  see  how  the  powder  rises  over  the  flame,  moves 
up  to  near  the  top  of  the  water,  then  to  one  side  and  down  again.  When 
you  stand  in  front  of  an  open  fireplace  by  what  process  are  you  warmed? 
What  process  of  heat  transfer  is  involved  in  warming  yourself  by  a  hot-air 
furnace?  By  a  hot- water  system?  112.  Draw  a  diagram  of  a  hot-air  furnace 
in  a  house,  showing  the  course  of  the  pipes.  113.  Construct  a  model  of  a 
hot-water  system  for  heating  a  house.  (Optional.) 

What  is  fire. — 114.  Examine  a  6-inch  strip  of  magnesium  ribbon  or 
wire.  Note  that  it  is  a  metal,  fairly  tough,  lustrous,  and  elastic.  Weigh 
it  as  accurately  as  possible  (see  p.  97).  Hold  one  end  of  the  piece  in  a  pair 


60  GUIDE  IN  PHYSICAL  NATURE-STUDY 

of  forceps  and  light  the  other  end  with  a  match.  Hold  the  burning  metal 
over  a  piece  of  dark  paper  to  catch  the  product.  Weigh  this  stuff  accu- 
rately together  with  any  unburned  ribbon  still  held  in  the  forceps.  Examine 
this,  rubbing  it  between  the  thumb  and  fingers.  In  what  ways  is  it  different 
from  the  original  metal?  Evidently  something  has  been  going  on  that 
completely  changes  the  nature  of  the  substance  involved.  This  is  a  chemical 
change.  You  know  that  air  is  usually  necessary  for  a  fire.  When  you 
want  the  fire  in  a  stove  or  furnace  to  burn  more  briskly  you  do  what? 
But  we  may  readily  show  that  not  all  the  gases  of  the  air  are  involved 
when  something  burns.  115.  Crumple  up  a  sheet  of  paper  in  your  hand. 
Fk>3,t  it  on  a  saucer  nearly  full  of  water.  Light  it  and  when  it  is  burning 
well  set  an  empty  tumbler  down  over  it,  into  the  water,  and  let  the  mouth 
rest  on  the  saucer.  What  happens?  Can  you  tell  why?  What  fractional 
part  of  the  tumbler  is  filled  with  w,ater?  Evidently  only  a  part  of  the 

air  is  used  up  in  the  burning,  and  this  is  about per  cent  of  the  volume 

of  air.  (Why  is  this  estimate  not  accurate?)  The  gas  that  is  usually 
involved  in  burning  or  combustion  is  oxygen.  Which  was  heavier,  the 
magnesium  strip  or  the  product  produced  by  burning  it,  and  why? 
(Answer  this  after  the  next  experiments  are  completed.) 

To  make  oxygen. — 116.  Make  a  bend  in  each  end  of  a  1 5-inch  length 
of  glass  tubing,  about  ij  inches  from  the  end.  Let  each  bent  portion 
stand  at  an  angle  with  the  long  portion  of  the  tube  that  is  distinctly  less 
than  a  right  angle,  and  have  the  bent  ends  stick  out  on  opposite  sides  of 
the  long  portion.  Fit  one  end  of  this  delivery  tube  through  a  cork  that 
fits  the  mouth  of  a  good-sized  test  tube.  Put  a  teaspoonful  of  pulverized 
potassium  chlorate  mixed  with  half  as  much  manganese  dioxide  into  the 
test  tube.  Hang  this  on  a  ring  stand  so  that  the  flame  can  be  applied  to 
its  lower  end.  Let  the  other  end  of  the  delivery  tube  lie  on  the  bottom  of 
a  fairly  deep  pan,  its  open  end  pointing  up.  Fill  this  pan  nearly  full  of 
water.  Sink  a  wide-mouthed  8-ounce  bottle  in  this  water  so  that  it  will 
fill  full.  Then  lift  it  up,  keeping  the  mouth  below  water,  and  support  it 
in  position  with  the  mouth  over  the  end  of  the  delivery  tube.  Heat  the 
mixture  in  the  test  tube.  The  air  will  bubble  out  first.  Move  the  end  of 
the  delivery  tube  so  that  this  can  escape.  Oxygen  gas  will  bubble  out, 
shortly,  in  a  steady  stream.  Catch  this  in  the  bottle.  Fill  three  bottles. 
Cover  the  mouths  with  small  glass  plates;  and  lift  them  out  of  the  water, 
setting  them  right  side  up  on  the  table.  117.  Light  a  splinter  of  wood 
and  when  burning  well  blow  out  the  flame,  leaving  a  glowing  ember  on 
the  end.  Slide  the  glass  cover  of  one  bottle  to  one  side  and  stick  the  splinter 
in.  What  happens,  and  why?  118.  Take  a  J-inch  piece  of  soft-cored 
electric-light  carbon  and  dig  out  one  end  so  as  to  make  a  depression.  Fasten 


SOME  COMMON  APPLIANCES  OPERATED  BY  HEAT  6 1 

this  piece  on  a  wire  to  serve  as  a  handle  in  letting  the  carbon  down  into 
another  jar  of  oxygen.  Put  a  bit  of  sulphur  as  large  as  a  half-pea  in  the 
depression  of  this  "spoon,"  ignite  it  and  lower  the  "spoon"  into  the  jar 
of  gas.  What  happens? 

119.  Unravel  slightly  one  end  of  a  6-inch  length  of  woven  iron  wire 
picture  cord.  Fasten  a  bit  of  wood,  like  a  piece  of  broken  match,  in  the 
ravelings.  Light  the  wood  and  when  it  is  burning  well  stick  it  into  the 
third  jar  of  oxygen.  What  happens,  and  why? 

Spontaneous  combustion. — What  do  you  have  to  do  to  an  ordinary 
match  to  start  it  burning?  Rub  your  hand  briskly  over  your  coat  sleeve 
or  any  rough  cloth  for  a  minute.  What  is  noticeable?  How  did  the  Indians 
start  a  fire?  120.  Let  some  member  of  the  class  make  the  Indians'  fire 
stick  and  try  to  produce  fire  with  it.  Some  substances  take  fire  at  ordinary 
temperatures.  Phosphorus  is  one  such.  121.  Take  a  small  piece  of 
this  out  of  the  fluid  in  which  it  is  kept  in  a  bottle,  using  a  forceps  with  which 
to  handle  it,  and  lay  it  in  an  evaporating  dish  on  the  table.  In  a  few  minutes 
it  begins  to  smoke  perceptibly  and  promptly  bursts  into  flame.  The  igni- 
tion point  is  below  ordinary  room  temperature.  The  ignition  point  of 
wood  is  relatively  high  so  that  the  bit  that  is  to  be  a  match  is  dipped  into 
a  substance  that  has  an  ignition  point  low  enough  to  be  attained  by  brief 
friction.  The  ignition  point  of  sulphur  is  low  enough  so  that  it  may  be 
ignited  with  a  match.  It  burns  much  more  freely  in  an  atmosphere  of  pure 

oxygen.  The  greater  the  supply  of  oxygen  the 

combustion  occurs.  The  ignition  point  of  iron  is  so  high  that  it  will  not 
burn  in  ordinary  air  at  all  readily  but  does  burn  in  an  atmosphere  of  oxygen. 

When  the  sulphur  burned  in  the  atmosphere  of  oxygen  dense  fumes 
filled  the  bottle.  When  magnesium  was  burned  in  air  a  new  substance 
was  formed.  The  chemist  tells  us  that  when  the  temperature  is  sufficiently 
high  to  start  up  the  action  the  tiny  particles  of  sulphur  unite  with  the 
tiny  particles  of  oxygen  and  thus  form  a  new  substance,  a  combination  of 
sulphur  and  oxygen  known  as  an  oxide  of  sulphur.  This  constitutes  the 
dense  fumes  in  the  bottle.  Thus  the  magnesium  and  oxygen  unite  and 
form  an  oxide  of  magnesium.  Iron  and  sulphur  and  magnesium  and 
oxygen  are  called  elements  because  they  cannot  be  broken  up  ordinarily  into 
simpler  substances.  But  the  potassium  chlorate  used  in  making  oxygen  is  a 
compound,  for  we  could  get  oxygen  from  it  and  still  have  a  residue  left. 
Thus  when  the  hydrogen  was  made  to  fill  our  soap  bubbles  the  granulated 
zinc  shoved  the  hydrogen  out  of  its  combination  with  chlorine  gas  of  the 
chlorhydric  acid  (HC1)  and  took  its  place,  making  chloride  of  zinc. 

We  think  then  of  a  chunk  of  potassium  chlorate  as  a  thing  which  can 
be  subdivided  into  smaller  bits  of  potassium  chlorate  and  then  into  smaller 


62  GUIDE  IN  PHYSICAL  NATURE-STUDY 

and  smaller.  Finally  we  think  of  a  little  bit  smaller  than  we  can  see  that 
cannot  be  broken  apart  and  still  be  potassium  chlorate.  This  is  what  the 
physicist  calls  a  molecule.  Chlorhydric  acid  may  be  separated  into  hydro- 
gen and  chlorine;  these  still  smaller  units  which  unite  to  make  a  molecule 
of  chlorhydric  acid  are  atoms,  and  in  this  case  one  atom  of  hydrogen  unites 
with  one  of  chlorine  (HC1). 

Such  a  union  is  not  always  a  one-and-one  affair,  for  atoms  seem  to 
have  hands  or  bonds  or  lines  of  force  by  which  they  take  hold  of  other 
atoms.  Some  atoms  have  two,  others  four,  some  only  one.  Thus  oxygen 
has  two,  hydrogen  only  one.  When  hydrogen  burns  the  substance  formed 
is  H2O  or  water.  Sulphur  has  four.  When  it  burns  the  substance  formed 
is  SO2.  Chemists  have  devised  a  sort  of  shorthand  for  writing  out  these 
reactions  and  indicate  the  elements  by  the  initial  letter  of  their  English 
or  sometimes  their  Latin  names.  In  case  two  or  more  elements  begin  with 
the  same  letter,  it  is  necessary  to  use  in  such  cases  two  letters  from  the 
name;  thus  C  is  carbon;  Cl,  chlorine;  N  is  nitrogen;  Na,  sodium  (Latin, 
natrium).  Thus  when  sulphur  burns  the  reaction  is  written: 


the  crinkled  line  over  the  latter  symbol  showing  that  it  is  a  gas. 

=  ZnCl2+2H. 


The  burning  candle.  —  122.  Light  a  candle   and   observe  (i)  that  the 
solid  material  of  the  candle  is  changed  to  a  liquid;  (2)  that  this  liquid  is 
conducted  up  the  wick  of  the  candle;  (3)  that  it  is  changing  to  a  bluish 
substance  at  the  center  of  the  flame;  (4)  as  this  burns  it  forms  the  outer 
part  of  the  flame.    Lay  a  piece  of  white  paper  on  the  flame  and  hold  it 
just  long  enough  for  it  to  scorch  a  bit  without  burning.     What  do  you 
learn  from  examining  the  scorch  on  the  paper?     123.  Hold  a  short  length 
of  quite  small  glass  tubing  with  one  end  in  the  bluish  part  of  the  flame 
and  the  other  end  above  and  to  one  side  of  the  flame.    The  purpose  is  to 
conduct  some  of  this  blue  material  through  the  tubing.    Can  you  light  it 
as  it  comes  out  of  the  upper  end  of  the  tube?     Here  evidently  the  solid 
material  of  the  candle  is  first  changed  to  .....................  ,  then  to  ...................  , 

and  when  burned  it  goes  off  into  the  air  as  gas.  Set  a  piece  of  candle  in 
the  bottom  of  a  wide-mouthed  bottle.  Light  it  with  a  long  splinter  and 
cork  the  mouth  of  the  bottle.  What  happens,  and  why? 

124.  Put  a  piece  of  slacked  lime  as  large  as  a  bean  into  a  tumbler  of 
water.  Let  it  stand  for  one  hour,  stirring  it  occasionally,  then  let  it  stand 


SOME  COMMON  APPLIANCES  OPERATED  BY  HEAT  63 

to  settle  until  the  water  is  clear.  Pour  off  the  clear  water  into  a  tumbler. 
125.  Pour  half  of  this  into  the  bottle  with  the  candle.  Uncork  the  latter 
as  little  as  possible  to  accomplish  this.  Shake  it  up  and  then  note  the 
color  of  the  limewater.  This  is  a  commonly  used  test  for  one  of  the  gases 
resulting  from  the  burning  of  carbon,  namely,  carbon  dioxide. 

126.  Blow  through  a  length  of  glass  tube,  the  end  of  which  is  dipped 
into  the  remainder  of  the  limewater.  What  do  you  learn? 

Gunpowder. — Sometimes  the  volume  of  gas  formed  when  solid  sub- 
stances burn  is  very  great.  127.  Mix  one  part  of  sulphur,  one  of  powdered 
charcoal,  three  of  potassium  chlorate.  Put  as  much  of  this  as  will  go  on 
a  penny  on  a  piece  of  iron.  Touch  a  match  to  it.  The  potassium  chlorate 
is  mixed  with  the  sulphur  and  charcoal  to  furnish  an  abundant  supply  of 
oxygen  so  that  the  charcoal  and  sulphur  can  burn  very  freely,  forming  a 
great  volume  of  gas.  This  substance  that  we  have  made  is  really  gunpowder. 
If  set  off  in  a  confined  space  the  gases  formed  will  break  out,  their  pres- 
sure is  so  great. 

Making  coal  gas. — 128.  Break  up  a  small  piece  of  soft  coal  (or  pine 
wood)  into  bits  and  fill  the  bowl  of  an  ordinary  clay  pipe,  such  as  children 
use  for  blowing  soap  bubbles,  two- thirds  full.  Then  plug  the  opening  of 
the  bowl  with  a  piece  of  clay  or  with  plaster  of  Paris  mixed  with  water  to 
the  consistency  of  putty.  If  the  latter  is  used,  let  it  stand  for  a  few  minutes 
to  harden  in  the  pipe.  Heat  the  bowl  of  the  pipe  over  the  flame  of  the 
Bunsen  burner  or  alcohol  flame.  At  first,  water  vapor  will  pour  out  of  the 
opening  in  the  stem  of  the  pipe;  soon,  however,  gas  will  be  delivered. 
Light  this  and  note  that  it  burns  with  a  flame  much  like  a  candle  flame. 
Soft  coal  contains  much  carbon  and  some  hydrogen.  As  these  substances 
burn,  what  would  be  the  products  of  combustion  ?  After  the  gas  is  all 
driven  off,  take  out  the  clay  or  plaster  plug  and  examine  the  residue  in 
the  pipe.  What  is  it? 

Gas  burns  ordinarily  with  a  yellow  flame  because  the  air  is  not  thor- 
oughly mixed  with  the  gas  and  some  of  the  unburned  carbon  freed  from 
the  gas  glows  in  the  heat.  If  air  is  mixed  with  the  gas  before  lighting  the 
mixture  then  the  combustion  is  much  more  complete  and  the  flame  is  much 
hotter,  hence  the  mixer  on  the  gas  burner  that  produces  the  blue  flame. 
129.  Turn  the  collar  on  the  Bunsen  burner  to  see  the  effect  and  explain 
the  result.  Introduce  an  old  saucer  into  the  flame  both  when  it  is  blue 
and  when  it  is  yellow.  What  deposits  on  the  saucer? 

The  gas  engine. — The  gas  generated  above  burns  steadily  in  the  open 
air.  If,  however,  gas  and  air  are  mixed  in  a  confined  space  before  the  gas 
is  ignited,  the  combustion  takes  place  instantly,  quantities  of  hot  gas 
are  formed,  and  the  result  is  an  explosion.  Advantage  is  taken  of  this 


64  GUIDE  IN  PHYSICAL  NATURE-STUDY 

in  the  gas  engine,  in  which  the  force  of  the  explosion  is  used  to  furnish 
motive  power.  This  may  be  readily  illustrated  as  follows.  130.  Make  a 
hole  in  the  side  of  a  small  tin  coffee  or  tea  pot  near  the  bottom,  through 
which  may  be  run  the  metal  tube  of  the  Bunsen  burner.  On  the  opposite 
side,  halfway  up,  punch  another  hole  as  large  as  a  pencil.  Insert  the 
Bunsen  burner  in  the  lower  hole.  Tie  a  piece  of  clock  spring  to  the  handle 
so  that  it  will  press  lightly  on  the  cover  to  keep  it  closed.  Turn  on  the 
gas  and  hold  a  candle  flame  or  match  beside  the  small  hole,  halfway  up 
the  side.  Successive  explosions  blow  the  cover  up,  but  the  spring  closes 
it  each  time. 

Toy  gas  engines  are  commonly  sold  as  children's  toys.  131.  Operate 
one.  These  are  single-cylinder  engines;  therefore  the  wheel  goes  around 
with  a  rather  jerky  motion.  The  automobile  gas  engine  has  several  cylin- 
ders, the  explosions  occurring  in  them  in  succession,  so  that  power  is  applied 
to  the  crank  at  such  frequent  intervals  as  to  produce  a  steady  motion. 
The  mixture  of  gas  (vaporized  gasoline)  and  air  is  ignited  by  an  electric 
spark.  Write  to  some  automobile  concern  for  a  catalogue  that  will  illustrate 
their  engine.  Insert  it  on  the  opposite  page,  or  else  draw  your  own  diagram 
of  such  an  engine. 

Steam  engines. — In  the  steam  engine  the  piston  is  driven  back  and 
forth  by  the  expansive  force  of  steam  under  pressure,  operating  on  the 
piston  head.  It  is  necessary  that  there  be  some  device  to  cut  off  the  inlet 
of  steam  at  one  end  of  the  cylinder  when  the  piston  head  has  been  driven 
as  far  as  possible,  and  to  let  in  the  steam  at  the  opposite  end  to  drive  the 
piston  head  back  again.  Furthermore,  there  must  also  be  some  way  of 
letting  the  steam  out  from  the  end  of  the  cylinder  toward  which  the  piston 
head  is  moving. 

See  a  toy  steam  engine  work.  Examine  the  model  of  the  working 
parts  of  an  engine  or  see  the  paper  model  in  Nelson's  Encyclopedia  article 
"Steam  Engine."  132.  Make  a  cardboard  model  with  movable  parts  to 
illustrate  the  method  of  operation  of  the  piston  in  the  cylinder,  the 
eccentric  cut-off  and  the  exhaust  valves. 

A  glass  model  may  be  made  and  operated  by  air  blown  into  it  as  follows : 

133.  Select  a  6-inch  length  of  large  glass  tubing  an  inch  or  so  in 
diameter,  or  use  an  8-dram,  wide-mouthed  homeopathic  vial.  Bore  four 
holes  in  the  side  of  the  tube  or  vial,  two  on  one  side,  two  on  the  other, 
setting  them  about  i  inch  from  the  ends.  The  hole  may  be  bored  by  using 
the  tip  of  a  round  file  or  drill  kept  wet  with  camphor  gum  dissolved  in 
turpentine.  Pulverize  the  camphor  gum  coarsely  and  put  it  into  the 
turpentine,  letting  it  stand  for  several  hours  before  using.  Two  of  these 
holes  will  be  inlets  for  the  air  and  two  will  be  outlets  for  the  exhaust. 


SOME  COMMON  APPLIANCES  OPERATED  BY  HEAT  65 

Steam  chest. — Cut  glass  so  as  to  make  a  small  box,  the  inside  dimensions 
of  which  will  be  as  wide  as  the  outside  diameter  of  the  tube  or  vial,  and 
nearly  as  long  as  the  vial.  File  out  the  ends  of  the  box  in  a  curve  to  fit 
the  curve  of  the  tube  or  vial,  keeping  the  file  wet  with  the  camphor  solution. 
Fasten  the  box  together  with  glass  or  china  cement.  Let  this  harden  for 
twenty-four  hours.  Then  reinforce  all  corners  of  the  box  with  strips  of 
surgeon's  adhesive  tape.  Cut  from  a  piece  of  bamboo  fishing-pole  of  about 
the  same  diameter  as  the  vial  two  strips  an  inch  shorter  than  the  distance 
between  the  holes  bored  in  the  tube  or  vial.  These  will  serve  as  the  sliding 
valves  to  open  and  close  these  holes.  Bevel  their  upper  edges.  Bevel  the 
under  edges  of  four  narrower  strips  of  the  same  length  as  the  inside  of  the 
box  and  glue  these  latter  to  the  outer  surface  of  the  tube  or  bottle  so  that 
they  will  hold  the  wider  strips  between  them  when  these  latter  strips  are 
laid  on  the  surface  of  the  tube  or  vial  between  the  holes.  These  strips 
should  be  held  loosely,  so  as  to  allow  back  and  forth  movement. 

Piston. — Fit  a  slice  of  cork  or  a  short  section  of  a  spool  to  the  end  of 
a  wooden  piston  rod,  the  spool  or  cork  being  of  sufficient  size  to  move 
back  and  forth  in  the  bottle,  which  it  must  fit  fairly  snugly.  Cut  a  groove 
with  a  round  file  in  the  edge  of  the  cork  or  wooden  piston  head  and  bind 
with  string  so  as  to  make  the  contact  between  the  inside  of  the  bottle 
and  the  piston  head  fairly  air-tight.  The  wooden  piston  rod  should  be 
slightly  longer  than  the  bottle.  If  a  tube  has  been  used,  cork  both  ends 
with  a  thin  cork  so  that  the  holes  bored  in  the  tube  or  vial  will  not  be 
covered.  Bore  a  hole  in  the  center  of  one  of  these  just  large  enough  to 
allow  the  round  piston  rod  to  slip  through. 

Fasten  a  block  of  wood  about  ij  inches  square  and  J  inch  thick  by 
one  side  to  one  end  of  a  board  that  is  i  foot  long  and  about  3  inches  wide. 
Cut  a  V-shaped  notch  down  to  the  middle  of  this  block  on  its  upper  edge. 
The  ends  of  the  V  should  be  close  to  the  corners  of  the  block.  Fasten 
the  tube  or  vial  about  its  midpoint  to  this  block,  setting  it  in  the  V,  with 
two  of  the  holes  down  and  two  up.  In  line  with  the  center  of  the  tube 
or  vial  toward  the  other  end  of  the  board  set  up  a  block  on  which  may  be 
mounted  vertically  a  wheel  of  thin  wood,  its  diameter  in  the  plane  of  the 
long  axis  of  the  vial.  Attach  a  driving  rod  to  this  wheel  ij  inches  from 
its  center  and  connect  the  other  end  of  the  driving  rod  with  the  piston 
that  protrudes  from  the  cork  in  one  end  of  the  tube  or  vial. 

Devise  eccentric  rods  that  will  run  from  the  wheel  or  its  axis  to  the 
sliding  valves  that  cover  and  uncover  the  holes.  Think  out  how  these 
sliding  valves  are  going  to  work  before  you  make  your  attachment,  so  as 
to  have  them  work  at  proper  intervals.  File  out  the  front  end  of  the  glass 
box  a  bit  to  make  room  for  the  rod  that  attaches  to  the  sliding  valve. 


66  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Bore  a  hole  in  the  top  of  the  glass  box  large  enough  to  admit  a  small  glass 
tube.  Cement  in  an  inch  length  of  glass  tubing,  the  end  of  it  flush  with 
the  inside  of  the  box.  Through  this  tube  air  will  be  blown  into  the  steam 
box.  Cement  the  box  to  the  top  of  the  vial  and  reinforce  the  joint  with 
surgeon's  tape.  The  engine  should  be  ready  to  operate  now  by  blowing 
through  the  glass  tube,  to  which  a  length  of  rubber  tube  may  be  attached 
for  convenience.  Since  the  apparatus  is  made  of  glass  it  is  easy  to  see  the 
working  of  all  parts. 


MAGNETIC  AND  ELECTRIC  TOYS 

The  compass. — 134.  Take  a  compass  in  hand  and  note  how  it  is 
made,  and  if  the  needle  assumes  a  fixed  position  when  at  rest.  135.  Take 
a  couple  of  bar  magnets  and  note  how  they  behave  with  reference  to  each 
other.  Present  an  end  of  one  magnet  to  an  end  of  the  other;  try  the  opposite 
end.  Repeat  the  operation  several  times  until  you  can  state  a  law  that 
governs  the  behavior  of  the  magnets  with  reference  to  each  other. 
136.  Suspend  a  bar  magnet  so  that  it  will  hang  freely  by  a  very  fine  wire 
or  a  strand  of  non-twisted  fiber.  Let  it  stand  until  it  comes  to  rest.  What 
position  does  it  assume?  137.  Present  the  end  of  a  bar  magnet  to  the 
compass  needle  and  note  what  happens.  Try  the  other  end.  What  did 
you  make  when  you  hung  the  bar  magnet  on  the  fine  wire?  How  would 
you  state  the  law  governing  the  movement  of  the  compass  needle  when 
influenced  by  the  bar  magnet?  When  the  bar  magnet  is  suspended,  what 
influences  its  position,  determining  the  direction  it  assumes  when  quiet? 
What,  then,  would  you  call  the  earth? 

To  make  a  magnet  out  of  a  bar  of  soft  iron. — 138.  Dip  a  bar  magnet 
into  iron  filings.  What  happens?  Present  the  end  of  a  bar  magnet  to  the 
head  of  a  nail.  What  happens?  Present  the  tip  of  this  nail  to  the  head  of 
a  second  nail.  Try  touching  the  tip  of  the  second  nail  to  the  head  of  a  third 
nail.  139.  Take  a  knitting  needle  and  rub  one  end  of  it  vigorously  on  one 
end  of  a  magnet,  the  other  end  of  the  needle  on  the  other  end  of  the  magnet. 
Dip  one  end  of  the  knitting  needle  into  iron  filings.  What  happens,  and 
what  does  this  show?  140.  Take  a  piece  of  soft  iron,  like  an  ordinary  bolt; 
hold  it  parallel  to  the  earth's  axis  and  hit  it  repeatedly  with  a  hammer. 
Can  you  get  any  evidence  that  it  is  magnetized?  (Think  of  what  will  be 
the  most  delicate  test  for  this.)  Summarize  the  methods  by  which  magnets 
are  made.  Can  you  suggest  a  reasonable  explanation  of  what  occurs  in 
the  soft-iron  bar  to  change  it  to  a  magnet? 

Lines  of  magnetic  force. — 141.  Put  a  bar  magnet  under  a  piece  of 
stiff  card  that  is  sufficiently  large  to  cover  the  magnet;  sprinkle  fine  iron 
filings  on  the  surface  of  the  card  and  tap  the  card  gently  so  that  the  iron 
filings  will  have  a  chance  to  arrange  themselves  under  the  influence  of  the 
magnet.  142.  After  you  have  learned  how  to  accomplish  this  fasten  a 
piece  of  blueprint  paper  on  a  thin  drawing  board;  lay  the  drawing  board 
on  the  bar  magnet  and  tap  the  board  gently  until  the  iron  filings  are  well 
arranged.  Put  the  drawing  board  with  the  blueprint  paper  on  it  in  strong 

67 


68  GUIDE  IN  PHYSICAL  NATURE-STUDY 

sunlight  and  let  it  stand  until  the  paper  begins  to  assume  a  bronzed  tint. 
Remove  the  iron  filings  and  at  once  put  the  blueprint  paper  in  a  large  dish 
of  water  and  let  it  wash  in  running  water  for  ten  minutes.  Then  take  it 
out  and  spread  it  on  the  table  or  hang  it  up  to  dry. 

The  mysterious  pith  balls.— 143.  Fasten  two  little  balls  of  elder  pith 
each  on  a  fine  strand  of  silk.  Hang  them  so  they  will  be  side  by  side  and 
free  to  move.  Rub  a  glass  tube  with  a  piece  of  silk  and  bring  it  near  the 
balls.  What  happens?  After  the  balls  have  touched  the  glass  tubing, 
how  do  they  behave  with  reference  to  each  other?  Again  rub  the  glass 
with  the  silk,  touch  the  surface  of  the  glass  to  the  pith  balls,  and  then  rub 
a  stick  of  sealing  wax  with  the  silk  and  bring  it  near  to  the  balls.  What 
happens?  Bring  the  surface  of  the  silk  used  in  rubbing  the  sealing  wax 
near  to  the  balls.  What  happens?  Try  rubbing  the  glass  and  the  sealing 
wax  with  flannel,  and  touch  the  pith  balls  with  the  glass.  Then  bring  the 
sealing  wax,  also  rubbed  with  flannel,  near  them.  Continue  the  experi- 
ment until  you  can  state  the  law  that  governs  the  phenomenon.  Test  out 
your  law  to  see  if  you  can  always  tell  what  will  happen  when  the  balls 
are  brought  near  to  a  surface  that  has  been  rubbed  with  the  silk  or  the 
flannel.  What  conclusion  would  you  draw  from  these  experiments  regard- 
ing electricity? 

A  more  delicate  test. — 144.  Run  a  piece  of  naked  copper  wire  through 
the  cork  of  a  small  bottle  so  that  it  will  stick  down  halfway  in  the  bottle, 
with  3  or  4  inches  of  wire  above  the  cork  outside  of  the  bottle.  Make  a 
right-angled  bend  J  inch  from  the  end  of  the  wire,  inside  the  bottle,  and 
hang  on  the  bent  portion  a  strip  of  thin  tin  foil  2  inches  long,  suspending 
it  from  about  its  midpoint.  The  halves  of  the  strip  will  then  lie  face  to 
face.  Bend  the  free  end  of  the  wire  above  the  cork  so  as  to  make  a  little 
ball  of  wire  at  the  end.  Rub  the  glass  rod  with  the  silk  and  bring  the 
surface  of  the  rod  close  to  the  ball  on  the  end  of  the  wire.  What  happens? 
Touch  the  wire  ball  with  the  glass  rod;  then  bring  the  rubbed  surface  of 
the  silk  close  to  the  wire  ballr  Try  rubbing  the  glass  with  silk,  touch  the 
ball,  then  rub  the  sealing  wax  with  flannel  and  bring  it  near  the  ball.  This 
piece  of  apparatus  is  known  as  an  "electroscope."  How  would  you  use  it? 

Dancing  dolls. — 145.  Cut  out  of  tissue  paper  some  little  dolls,  f  inch 
long.  Lay  them  on  the  table  and  support  between  the  leaves  of  a  couple 
of  books  a  piece  of  window  glass  of  good  size  above  the  dolls  and  about 
i  inch  from  the  table.  Rub  the  upper  surface  of  the  glass  with  the  silk- 
What  happens?  Can  you  explain  it. 

The  electrophorus. — 146.  Fasten  an  old  phonograph  record  to  the 
underside  of  the. bottom  of  a  tin  pie  plate.  This  may  be  done  thus:  Make 
three  V-shaped  cuts  in  the  tin  plate  near  the  margin  with  the  point  of  the  V 


MAGNETIC  AND  ELECTRIC  TOYS  69 

out.  Bend  these  points  up  over  the  edge  of  the  record  so  as  to  hold  it  in 
place.  Set  the  tin,  rim  down,  on  the  table  and  rub  the  face  of  the  record  with 
silk.  Test  both  the  surface  of  the  record  and  of  the  silk  with  the  electro- 
scope. What  is  your  conclusion?  Again  rub  the  record  with  the  silk  and 
present  your  knuckle  to  the  edge  of  the  record.  A  slight  shock  may  be  felt 
and  if  the  air  is  dry  a  small  spark  may  be  drawn  from  the  record. 

To  make  lightning. — Frictional  electricity  may  be  accumulated  until 
quite  a  strong  charge  is  obtained  by  means  of  the  Ley  den  jar.  147.  To 
construct  this  take  a  wide-mouthed  8-ounce  bottle  and  cover  its  sides  and 
bottom  inside  and  out  with  tin  foil,  pasted  on.  Pass  an  1 8-inch  length  of 
naked  copper  wire  through  the  cork,  leaving  4  inches  protruding  from  the 
top.  Roll  up  3  inches  of  this  to  make  a  little  ball.  Bend  the  wire  below 
the  cork  so  that  it  will  be  in  contact  with  the  tin-foil  lining  when  the  cork 
is  in  the  mouth  of  the  bottle. 

148.  Rub  the  electrophorus  with  the  silk  and  then,  holding  the 
Leyden  jar  in  the  hand,  present  its  knob  to  the  edge  of  the  record  on  the 
electrophorus.  The  latter  will  discharge  into  the  Leyden  jar,  possibly 
showing  a  spark.  Repeat  this  a  number  of  times.  Why  does  the  charge 
in  the  jar  get  stronger  constantly,  and  why  does  an  equally  strong  charge 
of  the  opposite  sort  develop  on  the  outside  of  the  jar?  Strip  the  insulation 
from  8  inches  of  one  end  of  a  1 5-inch  insulated  copper  wire  and  from  i 
inch  at  the  other  end.  Bend  the  8  inches  of  naked  wire  about  the  tin 
foil  on  the  outside  of  the  jar  and,  holding  the  wire  by  the  insulated  portion, 
bring  the  other  end  close  to  the  knob  on  the  jar.  What  happens,  and  why? 
Why  call  this  lightning? 

The  frictional  electrical  machine  usually  consists  of  a  revolving  glass 
disk  against  which  brushes  rub  to  generate  the  electricity.  Other  metal 
brushes  take  off  the  positive  and  negative  electricity  to  two  Leyden  jars. 
When  quite  a  charge  has  accumulated,  the  knobs  of  the  two  jars  are  brought 
close  enough  together  to  permit  the  discharge  of  a  zigzag  spark.  149.  Such 
a  machine  may  be  built  by  the  pupils,  using  an  old,  large-sized  phonograph 
record  in  place  of  the  glass  disk,  and  homemade  Leyden  jars.  The  details 
of  construction  may  be  learned  from  descriptions  and  figures  in  any  book 
on  physics.  (Optional.) 

To  make  a  simple  battery. — -150.  Take  a  strip  i  by  3  inches  each  of 
sheet  copper  and  sheet  zinc.  Punch  a  hole  with  a  nail  near  one  end  of 
each  and  fasten  in  the  naked  end  of  a  6-inch  length  of  insulated  copper 
wire,  in  one  strip,  of  an  1 8-inch  length  in  the  other.  Twist  it  in  tightly  so 
as  to  make  intimate  contact  of  the  wire  and  the  sheet  metal,  or,  better 
still,  solder  it  in.  (A  cheap  soldering  set  with  directions  can  be  obtained 
from  any  hardware  house.)  Fill  a  tumbler  two-thirds  full  of  water  and 


70  GUIDE  IN  PHYSICAL  NATURE-STUDY 

add  two  tablespoonfuls  of  chlorhydric  acid  (or  twice  as  much  vinegar). 
Hang  the  metal  strips  over  the  opposite  sides  of  the  tumbler  so  that  they 
are  below  the  surface  of  the  acidulated  water.  Hydrogen  gas  promptly 
begins  to  discharge  from  one  metal  strip.  If  not  add  more  acid.  Bring 
the  ends  of  the  wires  together  and  note  if  there  is  any  spark  visible.  Hold 
the  ends  between  the  moistened  tips  of  thumb  and  finger  and  note  if  you 
feel  any  electric  current. 

From  which  metal  plate  is  the  hydrogen  given  off  most  freely  when 
the  tips  of  the  wires  are  in  contact?  Do  some  of  the  bubbles  move  from 
one  plate  to  the  other  in  the  acidulated  water?  If  so,  from  which  to  which? 

The  chemistry  of  the  reaction. — -We  have  already  noted  how  elements 
combine  to  produce  new  substances  (see  p.  61).  The  metal  or  positive 
element  usually  combines  with  the  non-metal  or  negative  element  to  form 
a  salt.  Thus  the  zinc  and  the  chlorine  combine  in  this  case,  the  zinc  re- 
placing the  hydrogen,  which  is  forced  out  of  the  chlorhydric  acid  (HC1) ,  and 
ZnCl2  is  formed.  The  chemical  equation  showing  the  reaction  is 
Zn+2HCl=ZnCl2-h2H. 

Hydrogen  is  a  substance  whose  atoms  have  each  a  single  bond  or 
line  of  attraction  by  which  it  is  held  to  other  atoms,  or,  as  the  chemist 
says,  it  is  monovalent.  Zinc  is  bivalent.  Chlorine  is  monovalent.  To 
write  chemical  equations  one  must  know  the  valency  of  the  elements. 
He  must  also  know  the  formulas  for  the  acids  that  enter  into  a  reaction. 
If  we  had  used  sulphuric  acid  (H2SO4)  instead  of  chlorhydric  the  substance 
formed  would  have  been  zinc  sulphate,  ZnSO4,  instead  of  zinc  chloride. 
The  acid  radical,  SO4,  is  known  to  have  a  valence  of  two  because  it  combines 
with  two  atoms  of  H,  each  with  a  valence  of  one.  Acids  are  named  accord- 
ing to  the  amount  of  oxygen  present. 

The  hydro-  acids,  like  hydrochloric  or  chlorhydric,  have  no  oxygen. 
What  is  the  name  of  HBr,  HI,  H2S?  Knowing  the  -ic  acid,  like  HC1O3, 
chloric  acid,  you  can  always  give  the  formulas  of  others  of  the  same  series, 

for  the  per ic  acid,  like  HC1O4,  perchloric  acid,  has  one  more  atom  of 

O  than  the  -ic  acid;  the  -ous  acid,  like  HC1O2,  or  chlorous  acid,  has  one 

less  atom  of  O,  and  the  hypo ous  acid,  like  HC1O,  or  hypochlorous 

acid,  has  two  less  than  the  -ic  acid. 

The  salts  formed  from  the  acids  are  readily  named: 

Hydr-  acids  give  -ide  salts.  NaCl  is  sodium  chloride, 
-ous  acids  give  -ite  salts.  NaClO2  is  sodium  chlorite, 
-ic  acids  give  -ate  salts.  NaClO3  is  sodium  chlorate. 

per ic  acids  give  per ate  salts.     NaClO4  is  sodium  perchlorate. 

hypo ous  acids  give  hypo ite  salts.    NaCIO  is  sodium  hypochlorite. 

Name  ZnCl2,  ZnSO4,  ZnSO3,  ZnSO2,  ZnSO5. 


MAGNETIC  AND  ELECTRIC  TOYS  71 

Movement  of  the  electrons. — We  conceive  of  the  atom  as  a  sort  of  solar 
system.  It  has  a  central  positively  charged  nucleus  around  which  revolve 
particles  of  negative  electricity  or  electrons.  Some  substances  tend  to  lose 
one  or  more  of  these  electrons,  in  which  condition  they  can  hold  more  nega- 
tive electricity  and  so  manifest  an  attraction  for  it,  and  are  said  to  be 
positive.  Others  take  on  extra  negative  particles  and  so  attract  the  posi- 
tive substances.  The  number  of  electrons  lost  or  gained  is  indicated  in 
terms  of  valence  (see  p.  70).  Thus  if  the  positive  nucleus  of  the  atom  of 
some  substance  holds  two  less  electrons  than  it  has  positive  charges,  that 
substance  is  said  to  be  positive  and  to  have  a  valence  of  two.  In  the 
violent  chemical  action  going  on  in  the  battery  electrons  are  set  free.  They 
pass  to  the  zinc  plate,  up  the  wire,  and  back  to  the  solution  by  the  copper 
plate.  The  zinc  plate  is  usually  designated  the  negative  electrode  and  the 
copper  plate  the  positive  electrode.  Furthermore  it  has  become  customary 
to  regard  the  current  as  flowing  outside  the  cell  from  the  positive  to  the 
negative  electrode,  though  the  electrons  move  in  the  opposite  direction. 

Why  the  simple  battery  stops  working. — The  simple  battery  made  above 
soon  ceased  to  give  a  current.  The  copper  strip  becomes  covered  with 
hydrogen  bubbles  that  are  bad  conductors  of  electricity.  Then,  too, 
impurities  in  the  common  sheet  zinc  or  copper  set  up  local  currents  between 
the  impurity  and  the  pure  metal.  These  difficulties  are  avoided  by  using 
purer  strips  of  metal,  by  surfacing  the  zinc  with  mercury,  and  by  using 
other  solutions  than  the  sample  acid,  solutions  which  contain  an  excess  of 
oxygen  that  unites  with  the  liberated  hydrogen  and  so  prevents  its  accumu- 
lation on  the  copper  or  other  negative  plate. 

The  gravity  cell  is  made  as  follows:  151.  Attach  insulated  wires  to 
the  zinc  and  copper  strips  as  before.  Lay  the  copper  strip  on  the  bottom 
of  the  tumbler  and  throw  on  it  a  heaping  teaspoonful  of  copper  sulphate 
crystals.  Fill  the  tumbler  nearly  full  of  water  and  add  a  few  drops  of 
sulphuric  acid.  Suspend  the  zinc  strip  in  the  upper  part  of  the  water. 
The  sulphuric  acid  acts  upon  the  zinc,  making  zinc  sulphate,  which  dis- 
solves. The  zinc  sulphate  solution  is  light  and  remains  in  the  top  of  the 
tumbler  above  the  heavy  copper  sulphate  solution.  The  liberated  hydrogen 
moves  toward  the  copper  plate,  but  before  reaching  it  drives  out  the  copper 
of  the  copper  sulphate,  the  copper  depositing  on  the  copper  plate.  The 
zinc  and  copper  sulphate  waste  away  and  must  be  renewed  occasionally; 
the  zinc  sulphate  increases  and  deposits  as  crystals,  which  must  be  removed. 

Another  type  of  battery  uses  potassium  bichromate,  KaCr2O7,  to  take  up 
the  hydrogen.  152.  Make  enough  strong  solution  of  potassium  bichromate 
to  nearly  fill  a  tumbler.  Add  about  a  half-teaspoonful  of  strong  sul- 
phuric acid.  Fasten  insulated  wires,  bare  at  one  end,  to  a  rod  of  zinc 


72  GUIDE  IN  PHYSICAL  NATURE-STUDY 

or  zinc  strip  and  a  piece  of  electric-light  carbon.  Immerse  these  in  the 
solution  and  note  the  current.  The  sulphuric  acid  attacks  the  zinc.  The 
liberated  H  starts  toward  the  carbon  but  on  the  way  unites  with  some  of 
the  O  of  the  potassium  bichromate  solution,  reducing  the  bichromate  to 
a  chromate. 

The  dry  cell. — 153.  Pull  an  old  worn-out  dry  cell  to  pieces.  The 
black  powdery  substance  inside  is  largely  carbon  and  manganese  peroxide, 
which  was  originally  mixed  with  ammonium  chloride.  What  are  the  metals 
in  the  battery?  154.  Make  a  dry  battery  for  yourself. 

To  detect  an  electric  current  and  determine  the  direction  of  its  flow 
one  may  make  a  simple  form  of  the  galvanoscope.  155.  Set  a  compass 
on  the  table  and  bring  a  wire  through  which  a  current  is  running  over  the 
needle  and  parallel  to  it.  What  happens  to  the  needle?  Turn  the  wire 
about  so  that  the  current  is  flowing  over  the  needle  in  the  opposite  direc- 
tion. How  is  the  needle  affected?  Try  the  wire  in  both  positions  under 
the  compass  needle.  Make  a  statement  in  writing  on  the  opposite  page 
indicating  the  relation  of  the  behavior  of  the  needle  to  the  direction  of  the 
flow  of  the  current.  156.  When  you  are  riding  in  a  street  car  take  a 
compass  along  to  see  if  its  needle  is  deflected  by  the  current  passing  along 
the  trolley  wire  overhead. 

157.  Wrap  insulated  wire  a  dozen  times  about  some  cylindrical  object, 
like  a  quart  fruit  jar,  so  as  to  make  a  circular  coil  of  the  wire,  leaving  free 
ends  to  attach  to  the  battery.  Cut  a  strip  of  wood  wide  enough  for  the 
compass  to  stand  on  and  as  long  as  the  diameter  of  the  coil.  Fasten  this  strip 
into  the  coil,  tying  the  coil  to  its  ends,  the  face  of  the  strip  at  right  angles 
to  the  plane  of  the  coil.  Connect  the  free  ends  of  the  wires  to  a  battery  and 
place  the  compass  on  the  middle  of  the  wood  strip.  Is  the  needle  deflected 
more  vigorously  than  before?  Reverse  the  direction  of  the  flow  of  the 
current  through  the  coil.  How  does  the  needle  behave?  Write  out  a 
statement  to  cover  the  relation  of  the  needle's  behavior  to  the  direction  of 
the  current's  flow  in  the  coil. 

Electroplating. — 158.  Fasten  a  wire  to  a  strip  of  copper,  as  was  done 
in  making  the  simple  battery  (p.  69),  and  also  fasten  a  wire  to  a  3-inch 
length  of  old  electric-light  carbon  by  winding  it  tightly  about  one  end. 
Hang  these  in  a  tumbler  two-thirds  full  of  diluted  sulphuric  acid.  This 
again  makes  a  battery.  Test  its  current  with  the  galvanoscope.  Connect 
the  wires  so  that  a  current  will  flow.  The  acid  acts  rapidly  on  the  copper, 
not  at  all  on  the  carbon.  Which  is  now  the  positive  and  which  the  nega- 
tive electrode?  In  what  direction  is  the  electric  current  moving  in  the 
wires  connecting  the  electrodes  ?  In  what  direction  is  it  moving  in  the 
solution  in  the  tumbler  ?  Let  the  current  run  for  some  time  and  then  note 


MAGNETIC  AND  ELECTRIC  TOYS  73 

the  deposit  on  the  carbon.  What  is  it?  Evidently  the  electric  current 
passing  through  the  solution  is  capable  of  carrying  the  metal  from  one 
point  and  depositing  it  at  another.  Advantage  is  taken  of  this  in 
electroplating. 

159.  Fasten  a  strip  of  copper  and  an  iron  nail  each  on  a  length  of  copper 
wire.  Suspend  them  in  a  tumbler  containing  a  strong  solution  of  copper 
sulphate.  Connect  the  wires  to  the  poles  of  the  battery  so  that  the  current 
will  flow  in  the  solutipn  from  the  copper-plate  to  the  iron  nail.  In  time  the 
nail  will  be  copper-plated.  Use  two  pieces  of  electric-light  carbon  in 
place  of  the  copper  strip  and  iron  nail  in  the  experiment.  Does  the  copper- 
plating  go  on  as  before  ?  If  a  silver  salt  in  solution  instead  of  the  copper 
sulphate  solution  were  used  in  the  experiment  with  the  carbons,  what 
would  be  the  effect  ?  How  would  one  replate  a  spoon  the  silver  on  which 
was  wearing  off  ? 

To  make  an  electromagnet. — 160.  Wind  an  insulated  copper  wire 
(not  too  fine)  around  an  iron  spike  or  bolt  a  few  times.  Attach  the  ends 
of  the  wire  to  the  poles  of  the  battery  so  that  a  current  will  flow  through  it. 
See  if  the  bolt  will  pick  up  iron  filings.  Which  end  of  the  spike  is  the  N 
end  of  the  magnet?  (Devise  a  way  to  find  out.)  Unfasten  the  ends  of 
the  wire  on  the  battery  and  reverse  them  so  that  the  one  formerly  attached 
to  the  positive  pole  is  now  attached  to  the  negative  pole.  Is  the  same  end 
of  the  spike  the  north  end  now?  What  is  the  effect  of  many  turns  of  wire 
on  the  bolt  instead  of  few  ? 

.  To  make  a  telegraph  instrument. — -161.  Cut  two  blocks  of  J-  to  f- 
inch-thick  wood  3  inches  wide,  making  one  6  inches  long,  the  other  3  inches. 
Nail  the  shorter  one  on  one  end  of  the  larger  so  that  it  stands  upright  when 
the  longer  one  is  laid  flat  on  the  table.  Cut  a  J-inch-wide  strip  of  springy 
sheet  metal  3  inches  long.  To  one  end  tack  a  slice  of  cork  or  a  small  block 
of  wood.  Lay  the  strip,  cork  up,  on  the  midline  of  the  upper  surface  of 
the  long  block,  the  base  end  2  inches  from  the  upright  block.  Tack  down 
the  base  end  and  bend  the  strip  so  that  the  cork  end  is  J-inch  above  the 
wood  strip.  Set  a  tack  part  way  in  the  wood  under  the  cork  end  of 
the  metal  strip  so  that  when  the  strip  is  pressed  down  it  will  rest  on  the 
head  of  the  tack. 

Wrap  a  copper  wire  about  the  upper  two- thirds  of  a  3-inch  wire  nail 
many  times,  leaving  the  free  ends  of  the  wire  i  foot  or  so  long.  Drive  the 
nail  into  the  baseboard  close  up  to  one  edge  of  the  upright.  Another  nail 
is  to  be  fastened  horizontally,  its  head  just  over  the  head  of  the  upright 
nail.  Fasten  the  sharp  end  of  this  nail  into  a  loop  of  string  tacked  to  the 
upright.  Hold  the  head  just  off  of  the  upright  nail  by  a  small  rubber  band 
also  tacked  to  the  upright. 


74  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Fasten  one  naked  end  of  the  wire  that  is  wound  about  the  upright  nail 
to  the  tacked-down  end  of  the  metal  strip,  the  other  end  to  one  pole  of  the 
battery.  Connect  the  other  pole  of  the  battery  by  a  wire  to  the  tack  under 
the  cork  end  of  the  metal  strip.  As  the  "key"  is  pressed  down  on  the  tack 
the  "sounder"  should  click.  Why?  If  it  does  not  work  at  first,  adjust 
it  so  that  it  will. 

162.  Work  with  a  second  person  who  also  has  made  such  an  instru- 
ment and  change  the  wiring  so  that  by  the  addition  of  a  "switch"  on  each 
instrument,  which  switch  you  will  devise  and  apply,  the  sounder  of  one 
instrument  will  sound  when  the  key  on  the  other  is  operated,  and  vice 
versa. 

163.  Set  up  a  pair  of  commercial  telegraph  intruments,  if  these  are 
available,  and  operate  them.    Look  up  the  Morse  alphabet  code  and  try 
sending  a  message. 

Some  common  electric  appliances. — 164.  Examine  the  electric  bell  to 
see  how  it  works.  Connect  it  up  with  a  battery  to  see  it  operate.  Follow 
the  course  of  the  current  to  see  how  the  clapper  is  made  to  strike  the  bell. 
How  is  the  current  broken  so  that  the  clapper  springs  back?  Draw  a 
diagram  and  write  an  explanation  to  accompany  it. 

165.  Examine  the  electric  buzzer  and  connect  it  up  with  a  battery  to 
see  how  it  operates. 

166.  Examine  a  "knife  switch"  to  see  how  it  serves  to  "break"  a 
current  when  open,  to  "make"  the  current  when  it  is  closed. 

Introduce  the  knife  switch  between  the  battery  and  the  electric  bell, 
wiring  properly  so  that  bell  will  ring  when  the  switch  is  closed. 

167.  Examine  a  push  button  to  see  how  it  operates  to  make  or  break 
the  current.    Draw  a  diagram  and  write  out  an  explanation  of  the  way 
the  button  operates.     Connect  up  the  push  button  with  the  battery  and 
bell  (or  buzzer)  so  that  it  will  ring  the  bell  when  it  is  pressed. 

To  make  an  electric  motor. — 168.  Cut  a  block  of  ^-  to  f-inch-thick 
wood  3  inches  wide  and  4  inches  long.  This  block  will  serve  as  the  base. 
Drive  a  wire  nail  about  i\  inches  long  clear  to  the  head  through  its  center, 
perpendicular  to  the  face.  At  the  midpoint  on  each  side  set  up  a  3-inch  strip 
of  J-inch  stuff  about  J  inch  wide,  fastening  the  upright  strips  to  the  base  by 
means  of  brads  so  that  they  stand  upon  the  same  side  of  the  base  as  the 
wire  nail.  Bend  ten  or  a  dozen  p-inch  lengths  of  soft-iron  wire  or  an  iron  rod 
into  U-shapes.  Tie  these  U-shaped  wires  together  at  two  or  three  points. 
Then  wind  insulated  copper  wire  many  times  around  one  end  of  the  (J, 
covering  perhaps  i  inch  from  the  end  of  the  U.  Leave  the  end  of  the  in- 
sulated wire  free  for  a  foot  or  more  of  length,  so  that  it  may  be  attached 
as  indicated  below.  Carry  the  insulated  wire  across  to  the  other  end  of 


MAGNETIC  AND  ELECTRIC  TOYS  75 

the  U,  carrying  it  down  the  wooden  upright  under  the  base  and  up  the 
upright  on  the  other  side.  Then  wind  it  around  the  other  end  of  the  U, 
making  the  turns  in  the  reverse  direction  from  those  on  the  first  winding. 
Leave  a  foot  of  wire  free  again  to  make  attachment.  Take  a  cork  about 
an  inch  in  diameter  and  punch  a  hole  through  the  middle  large  enough  to 
receive  a  short  length  of  glass  tube. 

Cut  a  4-inch  length  of  glass  tube  of  sufficient  size  to  slip  on  the  upright 
nail.  Heat  this  at  its  midpoint  in  the  Bunsen  burner  until  it  is  soft.  Then 
pull  the  ends  apart,  heating  the  top  of  one  of  these  pieces  until  it  is  rounded 
off.  Shove  this  rounded  end  of  the  glass  tube  into  the  big  end  of  the  cork 
and  let  it  go  nearly  through  the  cork.  The  open  end  of  the  tube  is  to  be 
slipped  on  the  nail,  the  end  of  which  is  to  be  sharpened.  This  makes  a 
nearly  frictionless  bearing.  Cut  eight  or  ten  2-inch  lengths  of  the  soft- 
iron  wire  (or  one  of  iron  rod)  and  bind  them  together  by  wrapping  the  insu- 
lated copper  wire  around  them  many  times.  Leave  the  ends  of  the  wire 
sticking  out  about  i  inch.  Fasten  this  coil  with  its  wire  core  on  the  small 
end  of  the  cork  so  that  its  axis  is  at  right  angles  to  the  glass  tube.  The 
coil  with  its  contained  wire  should  be  bound  on  so  that  it  balances  as  nearly 
as  possible  when  the  cork  is  on  the  nail. 

The  commutator. — Cut  two  strips  of  sheet  copper  half  as  wide  as  the 
cork  is  long  and  a  little  shorter  than  half  the  circumference  of  the  cork  at 
its  midpoint.  Strip  the  insulation  off  from  the  ends  of  the  copper  wire  of 
the  coil  on  the  cork;  bring  these  down,  one  on  either  side  of  the  cork,  and 
place  on  top  of  each  of  them  one  of  the  strips  of  sheet  copper  bent  to  con- 
form to  the  curve  of  the  cork.  With  thread  bound  on  close  to  the  edge  of 
the  copper  strips  fasten  these  latter  on  the  cork  so  that  together  they 
nearly  encircle  it.  Their  ends  must  be  separated  by  a  distinct  space  and 
each  must  be  in  contact  with  only  one  of  the  wire  ends.  Cut  two  strips 
of  sheet  copper  about  \  inch  wide  and  if  inches  long.  Tack  one  of  these 
on  each  of  the  uprights  by  one  end.  The  other  end  should  lie  on  the  copper 
strips  on  the  cork.  Fasten  a  6-inch  length  of  copper  wire  with  the  insulation 
removed  from  each  end  to  each  of  these  copper  strips  at  the  point  where 
it  is  tacked  to  the  upright.  Twist  together  the  other  end  of  one  of  these 
wires  to  the  free  end  of  the  wire  coming  from  the  end  of  the  U  that  lies  on 
the  same  side  of  the  apparatus.  Solder  to  this  juncture  of  the  two  wires 
one  end  of  the  wire  that  is  to  run  to  the  switch  or  batteries  furnishing  the 
current. 

If  the  motor  has  been  properly  made  it  should  run  when  the  current 
is  sent  through.  It  may  need  considerable  current  if  the  parts  are  not 
nicely  adjusted  so  as  to  avoid  friction.  This  current  may  be  taken  from 
an  ordinary  electric-light  wire  by  unfastening  the  wires  from  the  electric- 


76  GUIDE  IN  PHYSICAL  NATURE-STUDY 

light  circuit  and  attaching  them  to  a  knife  switch.  For  fear  this  current 
may  prove  too  strong  and  burn  out  some  of  the  connections  it  is  well  to 
introduce  resistance.  This  may  be  done  as  follows: 

Resistance. — 169.  Fill  a  beaker  or  large  tumbler  with  water  to  which 
eight  or  ten  drops  of  hydrochloric  acid  are  added.  Fasten  one  wire  from 
the  motor  to  the  knife  switch  and  let  the  other  dip  into  the  acidulated  water 
in  the  tumbler.  Take  a  short  length  of  insulated  wire  and  remove  the  insu- 
lation from  an  inch  of  each  end.  Fasten  one  end  of  the  wire  to  the  knife 
switch  and  put  the  other  end  in  the  tumbler  of  acidulated  water  at  the 
opposite  side  from  the  wire  that  brings  in  the  current.  If  enough  current 
does  not  flow  to  run  the  motor,  add  a  little  more  acid  and  bring  the  wires 
gradually  nearer  together  until  there  is  sufficient  current. 

*  Examine  a  small  dissectible  model  of  the  commercial  motor  to  see  how 
it  is  wired  and  how  it  works. 

To  make  a  dynamo. — 170.  The  motor  made  above  may  be  altered  to 
serve  as  a  dynamo.  Break  the  connections  between  the  wires  running  to 
the  U-shaped  magnet  and  those  running  to  the  commutator.  The  former 
are  to  be  connected  directly  to  the  battery.  Before  this  is  done,  however, 
arrangements  must  be  made  to  rotate  the  cork  bearing  its  coil.  Put  a 
small  spool  on  the  glass  tube  just  below  the  cork,  or  use  a  thick  slice  of 
cork  the  edge  of  which  is  grooved  to  take  a  string  belt.  Clamp  the  base- 
board of  the  motor  to  the  table  or  nail  it  to  a  board.  Saw  out  a  circular 
board  from  f-inch  stuff,  making  it  8  or  10  inches  in  diameter.  Groove 
its  edge  with  a  round  file  so  that  it  will  take  the  string  belt.  Bore  a  hole 
in  its  center  and  fasten  it  by  a  nail  horizontally  to  a  block  that  may  be 
clamped  to  the  table  or  nailed  to  the  same  board  that  the  motor  is  on. 
Set  it  near  the  motor  so  that  a  string  or  a  leather  shoe  string  may  be  tied 
about  its  edge  and  about  the  spool  or  cork  on  the  motor  axle  to  serve  as 
a  belt.  Put  a  nail  near  the  edge  of  this  wood  wheel  for  a  handle  so  that  the 
wheel  may  be  turned  rapidly.  This  will  make  the  coil  on  the  cork  of  the 
old  motor  whirl  very  rapidly.  Connect  up  the  wires  to  the  U-shaped 
magnet  with  a  battery.  Connect  the  wires  from  the  commutator  to  the 
galvanoscope.  Turn  the  wheel  to  rotate  the  coil  in  the  cork.  The 
galvanoscope  will  show  a  current  if  all  connections  are  good. 

The  principle  upon  which  the  dynamo  works  may  be  readily  illustrated 
by  the  following  experiments: 

171.  Roll  a  piece  of  paper  4  inches  wide  and  10  or  12  inches  long  so  as 
to  make  a  paper  tube  4  inches  long  and  i  inch  in  diameter.  Wind  insulated 
copper  wire  (about  No.  18  or  finer)  thirty  or  forty  times  around  the  paper 
tube,  thus  making  a  wire  coil  on  the  outside  of  the  tube.  Connect  the 
ends  of  this  wire  with  the  galvanoscope,  set  a  yard  or  so  from  the  coil. 


MAGNETIC  AND  ELECTRIC  TOYS  77 

Watching  the  needle  of  the  galvanoscope,  thrust  a  bar  magnet  quickly 
into  the  paper  tube.  Pull  it  out  again.  'Reverse  the  magnet  and  thrust 
in  its  other  end.  Try  thrusting  the  magnet  in  the  reverse  end  of  the  coil. 
Record  the  results  for  each  of  these  tests.  This  shows  in  general  that 
when  the  turns  of  a  wire  coil  cut  through  the  lines  of  force  of  a  magnetic 
field,  a  current  is  generated.  Can  you  state  the  relation  of  the  direction 
of  the  current  to  the  way  in  which  the  turns  run  in  the  coil? 

172.  Take  a  strip  of  paper  6  inches  long  and  2  inches  wide.    Make  a 
paper  tube  2  inches  long  on  your  pencil.    Remove  the  pencil  and  wind 
upon  the  tube  a  coil  of  insulated  wire,  leaving  ends  3  inches  long.    Stick 
these  ends  through  a  large  flat  cork  so  that  the  coil  stands  above  its  upper 
surface  and  parallel  to  it.    Attach  to  the  bare  ends  of  the  wires,  close  to 
the  bottom  of  the  cork,  strips  of  copper  and  zinc.     Set  the  cork  on  the 
surface  of  dilute  sulphuric  acid  in  a  tumbler.    A  current  should  now  be 
flowing  through  the  coil.    Present  the  end  of  a  bar  magnet  to  one  of  the 
coil  ends.     What  happens?    Try  the  other  end  of  the  magnet.     What 
position  does  the  axis  of  the  coil  assume  if  allowed  to  stand  for  a  few 
moments  undisturbed?     State  your  conclusion. 

Can  you  explain  now  how  the  dynamo  above  works,  and  can  you 
predict  in  what  direction  the  current  is  flowing  from  it? 

173.  Examine  a  small  commercial  dynamo  and  follow  the  course  of 
the  wiring.    Can  you  explain  how  it  works,  and  why? 

To  make  an  electric  toaster. — 174.  Take  a  block  of  f-inch  wood  about 
6  inches  square  and  tack  a  6-inch  square  of  asbestos  board  to  one  face. 
Cut  two  strips  of  the  heavy  asbestos  board  ij  by  6  inches.  Tack  one  of 
these  to  each  end  of  the  board  so  that  the  6-inch  edge  will  stand  up  about 
|  inch  above  the  asbestos  board.  Make  j-inch-deep  cuts  every  half-inch 
on  these  edges.  Take  about  90  inches  of  No.  24  iron  wire  and,  leaving 
3  inches  free  at  one  end,  insert  the  wire  into  the  cut  nearest  the  end  of  one 
6-inch  strip.  Carry  the  wire  to  the  corresponding  cut  on  the  strip  at  the 
other  end.  Bend  the  wire  and  put  it  into  the  next  cut  at  this  end  and 
carry  it  back  to  the  corresponding  cut  at  the  end  where  the  wiring  began. 
Continue  to  weave  the  wire  back  and  forth  until  all  the  cuts  are  filled. 
Fasten  insulated  copper  wires  to  the  free  ends  to  connect  with  the  current 
which  is  to  heat  this  iron  wire.  Take  5^  feet  of  No.  18  iron  wire  and  make 
four  turns  of  this  wire  around  the  board  from  end  to  end,  spacing  the 
turns  ij  inches.  These  wires  will  rest  on  top  of  the  asbestos  strips,  not 
set  in  the  cuts.  They  will  be  J  inch  above  the  wire  that  is  to  be  heated  and 
on  them  the  bread  to  be  toasted  will  be  laid. 

Connect  up  the  apparatus  with  the  incandescent  current,  putting  in 
resistance  as  was  done  in  case  of  the  motor.  The  iron  wires  should  heat 


78  GUIDE  IN  PHYSICAL  NATURE-STUDY 

red  hot.  The  principle  here  used  is  the  same  as  that  applied  in  electric 
heaters,  electric  irons,  etc. 

An  experiment. — 175.  Make  a  coil  of  a  dozen  turns  of  No.  30  or 
finer  insulated  copper  wire  around  the  bulb  of  a  thermometer.  Let  the 
current  flow  from  a  battery  through  the  wire  for  one  minute,  noting  the 
rise  of  the  mercury  in  that  time.  Use  the  same  length  of  No.  18  wire  and 
make  the  same  number  of  turns  around  the  bulb.  Connect  with  the  same 
battery  and  let  the  current  run  one  minute.  What  is  the  rise  in  temperature 
now?  State  your  conclusion. 

Resistance. — An  electric  current  in  passing  through  a  body  meets 
some  resistance,  somewhat  as  water  passing  through  a  pipe  is  retarded  by 
the  friction  on  the  sides  of  the  pipe.  (Remember  that  in  the  fountain  we 
made,  p.  50,  the  water  did  not  rise  as  high  as  its  level  in  the  funnel.)  The 
greater  the  resistance  the  more  energy  is  used  in  overcoming  it,  and  so  is 
transformed  into  heat.  Why  do  we  use  iron  wire  in  the  toaster  and  why 
does  the  experiment  with  the  thermometer  above  give  the  results  seen? 
(Recall  the  experiments  on  heat  conduction,  p.  57.) 

Pressure  and  rate  of  flow. — Name  some  substances  that  you  know  to  be 
good  electrical  conductors,  some  that  are  non-conductors.  In  the  latter  the 

is  so  high  that  practically  no  current  flows  through  them. 

Resistance  is  expressed  in  terms  of  ohms.  The  ohm  is  about  the  resistance 
offered  by  9 . 3  feet  of  No.  30  (American  gauge)  copper  wire.  To  overcome 
high  resistance,  high  electric  pressure  must  be  used.  Electric  pressure  is 
expressed  in  terms  of  volts.  Just  as  with  liquids,  the  greater  the  pressure 
the  more  the  flow,  so  with  electric  currents,  other  things  being  equal. 
The  unit  that  measures  the  rate  of  flow  is  the  ampere,  and  it  is  defined  as 
that  amount  of  current  which  flowing  through  a  standard  solution  of 
silver  nitrate  (as  in  silver-plating)  will  deposit  a  specified  amount  of  silver 
(0.001118  grams)  per  second.  The  electric  pressure  or  electromotive  force 
that  will  give  a  current  of  one  ampere  against  a  resistance  of  one  ohm  is 
called  a  wit. 

It  is  found  that  a  current  of  one  ampere  working  under  a  pressure  of 
one  volt  will  do  work  equivalent  to  1/746  of  one  horse-power.  This  unit 
is  known  as  the  watt.  Therefore,  volts  X  amperes  -4-  746  =  horse-power. 

The  instrument  used  for  measuring  the  amount  of  current  flowing  in  a 
wire  is  called  an  ammeter.  It  is  built  like  the  galvanoscope  except  that  the 
end  of  the  compass  needle  moves  over  a  graduated  scale  marked  in  amperes. 
The  voltage  of  the  current  is  measured  by  a  similar  instrument,  the  -voltmeter. 
In  this  the  wire  used  is  fine,  so  as  to  offer  higher  resistance.  The  greater 
the  voltage  the  more  the  current  that  flows,  and  so  the  more  the  needle  is 
deflected.  Both  instruments  may  be  combined  in  one,  the  wltammeter . 


MAGNETIC  AND  ELECTRIC  TOYS  79 

Batteries  may  be  set  up  either  in  series  or  parallel.  In  the  former  case 
the  positive  element  in  one  is  connected  with  the  negative  element  of  the 
next,  and  the  wires  bringing  off  the  current  connect  with  the  remaining 
positive  pole  and  negative  pole.  When  connected  parallel,  the  wires  from 
all  negative  poles  are  twisted  together,  those  from  all  positive  poles  are 
similarly  twisted  together,  and  the  current  is  taken  from  these  bunches  of 
wires.  176.  Connect  up  two  batteries,  first  in  series,  secondly  parallel, 
and  measure  the  amperage  and  voltage  of  the  current  obtained  in  each 
case.  Record  the  results. 

Electric  lights. — -177.  Connect  up  a  small  incandescent  electric  light 
with  a  battery  (or  several  batteries  in  series  if  necessary  to  light  it).  Why 
is  the  filament  in  the  light  so  small?  What  is  the  advantage  of  using  a 
nitrogen-filled  bulb?  Measure  the  voltage  and  amperage  of  the  current 
that  is  used  to  light  the  little  incandescent  light  above.  Then  introduce 
the  voltammeter  between  the  lighted  bulb  and  the  negative  pole  of  the 
battery.  How  do  the  voltage  and  amperage  now  compare  with  that  of 
the  battery  when  the  light  is  not  in  the  circuit?  Connect  up  two  small 
incandescent  electric  lights  with  the  battery,  first  wiring  them  "in  series," 
then  ' 'parallel."  In  which  case  do  they  burn  most  brightly?  Introduce 
the  voltammeter  as  before  in  each  case.  Which  sort  of  wiring  uses  up  most 
current?  Which  reduces  the  voltage  most? 

The  arc  light. — 178.  Sharpen  two  soft  lead  pencils.  Cut  away  the  wood 
from  each  for  a  half-inch  back  from  the  point,  thus  laying  bare  the  lead. 
Twist  an  end  of  No.  18  copper  wire  tightly  around  the  lead  near  the 
wood  on  each  pencil.  Connect  the  other  ends  of  the  wires  to  the  dynamo 
(or  to  a  series  of  batteries).  Holding  one  pencil  in  each  hand,  bring  the 
points  together  and  then  separate  them  the  least  bit.  You  thus  produce 
a  miniature  arc  light.  What  makes  the  light  in  this  case? 

Examine  the  arc  light  on  the  projection  lantern.  179.  With  a  pair  of 
forceps,  the  handles  of  which  are  covered  with  glass  tubes  or  rubber,  hold 
a  sliver  of  iron  ore  in  the  flame  of  the  arc  between  the  carbons.  What 
happens,  and  why?  Could  you  "weld"  two  pieces  of  iron  in  the  flame? 

The  induction  coil. — -This  is  a  somewhat  expensive  bit  of  apparatus  to 
make,  yet  it  is  exceedingly  interesting,  for  it  is  one  of  the  essential  pieces 
in  the  wireless  outfit  and  may  be  made  to  yield  brilliant  electric  sparks 
and  vigorous  electric  shocks. 

180.  Obtain  a  pound  spool  of  No.  36  insulated  copper  wire,  all  in  one 
piece,  and  a  4-ounce  spool  of  No.  14.  Cut  a  dozen  or  so  lengths  of  large- 
size  soft-iron  wire  as  long  as  the  pound  spool  and  tie  them  together  in  a 
round  bundle.  Wind  on  this,  in  close-set  turns,  the  No.  14  wire  three 
layers  deep,  leaving  the  ends  of  the  wire  sticking  out  a  foot.  Cover  this 


8o  GUIDE  IN  PHYSICAL  NATURE-STUDY 

coil  with  a  layer  of  bicycle  tape.  This  should  make  a  roll  about  as  large  as 
the  core  of  the  spool  on  which  the  No.  36  wire  is  wound.  Saw  off  one  end 
of  this  spool  as  close  to  the  wire  as  you  can  without  cutting  its  insulation- 
Finish  trimming  off  the  wood  with  a  knife  so  that  the  wire  can  be  slipped 
off  the  spool  and  on  the  tape-wound  coil  made  above.  As  this  is  done  get 
hold  of  the  inner  end  of  the  fine  wire  and  pull  it  out  a  foot  to  make  connec- 
tions. Cut  off  the  other  end  of  the  spool  and  slip  the  two  ends,  their  centers 
cut  out  somewhat  if  necessary,  on  the  ends  of  the  coarse  wire  coil  to  keep 
the  fine  wire  in  place  as  it  was  on  the  spool. 

Mount  the  double  coil  on  a  base  horizontally,  carrying  the  ends  of  the 
fine  wire  to  two  binding-posts  set  6  inches  apart  on  the  baseboard,  each 
post  with  openings  and  screws  for  two  connections.  Set  in  one  of  these 
openings  on  each  post  a  coarse  copper  wire,  its  end  tipped  with  a  ball  of 
solder,  the  wires  adjusted  so  that  their  balls  are  close  together  but  not 
quite  in  contact. 

Rig  a  windlass  somewhere  on  the  baseboard,  made  of  a  spool,  and  set 
at  intervals  a  row  of  tacks  in  a  line  all  around  the  spool,  their  heads  sticking 
up  so  that  as  the  spool  is  rotated  the  tacks  catch  and  lift  one  end  of  a  springy 
metal  strip  off  the  head  of  an  upright  nail.  The  other  end  of  this  strip  is 
fastened  to  the  top  of  an  upright  post  set  near  the  windlass  and  one  of  the 
coarse  wires  from  the  coil  is  connected  to  it.  The  other  coarse  wire  runs  to 
one  pole  of  the  battery  of  two  dry  cells  connected  in  series.  The  other  pole 
of  the  battery  is  connected  to  the  wire  nail,  on  the  head  of  which  rests  the 
metal  strip. 

As  the  windlass  is  turned  the  current  sent  through  the  primary  coil  of 
coarse  wire  is  constantly  made  and  broken.  The  lines  of  magnetic  force 
appearing  and  disappearing  constantly  cut  the  secondary  coil  and  induce 
a  current  of  high  voltage  which  will  send  sparks  between  the  terminals. 
If  your  moistened  finger  tips  are  put  on  the  binding-post  of  the  secondary 
coil  you  will  receive  quite  a  shock. 

181.  This  coil  can  be  made  to  break  its  own  current.  Devise  and 
apply  a  modification  of  the  apparatus  that  will  accomplish  this. 


THE  CAMERA,  TELESCOPE,  MAGIC  LANTERN,  AND  SOME 
EXPERIMENTS  IN  LIGHT 

To  measure  the  candle  power  of  an  electric  light,  the  brightness  of  its 
light  is  compared  with  that  of  the  flame  of  a  "standard"  candle.  Any 
candle  flame  may  be  used  to  show  the  method,  though  the  results  will 
not  be  accurate  unless  a  "standard"  candle  is  used.  Two  or  three  pre- 
liminary experiments  are  necessary  to  show  the  principles  involved. 

Experiments. — 182.  Make  a  cut  in  the  small  end  of  each  of  two  corks 
perpendicular  to  the  end.  Set  two  similar  cards,  one  in  each  cork,  and  make 
a  pinhole  in  the  middle  of  each.  Set  them  on  the  table  i  foot  apart  and 
set  up  a  candle  so  that  when  looking  through  the  two  holes  you  can  see 
the  candle  flame.  Move  one  of  the  corks  a  little  to  one  side.  Why  can 
you  no  longer  see  the  light  of  the  flame?  If  the  shades  in  a  room  are 
drawn  when  the  sunlight  is  on  the  windows  and  a  small  hole  in  one  shade 
admits  a  ray  of  light,  the  course  of  the  beam  of  light  may  be  seen  as  it 
lights  up  floating  dust  particles.  What  sort  of  a  path  does  it  have?  Why, 
then,  does  an  object  throw  a  shadow? 

183.  Cut  an  inch-square  piece  of  cardboard.    Hold  it  3  inches  from 
a  candle  flame  or  an  electric  light.    Hold  another  large  piece  of  card  or 
paper  6  inches  from  the  light.    How  large  is  the  shadow  of  the  inch  square? 
Hold  the  larger  card  or  paper  9  inches  away.    How  large  is  the  shadow 
now?    The  light  that  is  thrown  on  the  one-inch  square  of  card  would,  if 

the  card  were  not  there,  cover square  inches  of  surface  at  twice  the 

distance  of  the  card  from  the  candle, square  inches  of  surface  at  three 

times  the  distance  of  the  card  from  the  candle.    The  intensity  of  the  illu- 
mination from  any  source  of  light  varies,  then,  inversely  as  the  square  of 
the from  the 

184.  Set  a  nail  vertically  into  a  small  block  of  wood.    Stand  this  on 
a  white  sheet  of  paper  on  the  table.    Light  an  electric  light  and  set  it 
several  feet  from  the  nail  so  that  the  latter  will  cast  a  shadow  on  the  white 
paper.    Light  a  candle  and  move  it  nearer  to  or  farther  from  the  nail 
until  the  shadow  it  casts  is  just  as  dark  as  that  cast  by  the  electric  light. 
Measure  the  distance  to  the  candle  at  this  point  in  inches  and  the  distance 
to  the  electric  light  in  inches.    What  is  the  candle  power  of  the  electric 
light? 

To  make  a  candle  burn  in  a  glass  of  water. — 185.  Set  a  large  clear 
piece  of  window  glass  vertically  on  the  table  and  support  its  edges.  Set 

81 


82  GUIDE  IN  PHYSICAL  NATURE-STUDY 

a  box  with  one  side  open  on  the  table,  its  open  side  in  front  of  the  glass. 
Hang  a  black  cloth  back  of  the  glass  about  as  far  as  the  open  side  of  the 
box  is  in  front  of  the  glass.  Set  a  tumbler  of  water  on  the  table  just  in 
front  of  the  black  cloth  and  opposite  the  open  box.  Light  a  short  length 
of  candle  and  set  it  in  the  middle  of  the  bottom  of  the  box.  Looking  down 
over  the  top  of  the  box  against  the  glass  plate,  you  may  move  the  tumbler 
of  water  until  the  candle  appears  burning  in  its  center.  This  will  seem 
mysterious  to  any  person  who  does  not  know  how  the  apparatus  is  set  up. 
Explain  the  phenomenon  yourself.  Measure  the  distance  to  the  glass 
plate  from  the  middle  of  the  tumbler  and  the  distance  from  the  candle  to 
the  glass  plate.  State  the  relative  positions  of  an  object  and  its  mirror 
image. 

Some  such  arrangement  as  that  in  the  foregoing  experiment  is  some- 
times used  in  the  theater  to  produce  the  ghost  in  such  plays  as  Hamlet. 
The  actor  impersonating  the  ghost  is  strongly  illuminated  in  a  room  over 
or  below  the  stage  and  opening  toward  it.  The  room  is  lined  with  black. 
A  large  plate  of  glass  near  the  front  of  the  stage  reflects  the  image  to  the 
audience.  The  "ghost"  can  walk  through  tables  and  chairs  on  the  stage, 
just  as  the  candle  flame  goes  into  the  water. 

The  angle  of  reflection. — 186.  Set  up  a  mirror  on  a  sheet  of  white 
paper  on  the  table.  Stand  the  nail  on  the  block  on  the  table.  Look  along 
the  surface  of  the  table,  your  eye  at  its  level,  until  your  eye  is  in  position 
to  see  the  nail  in  the  mirror.  Draw  a  line  on  the  paper  from  the  image 
toward  your  eye,  one  from  the  image  toward  the  nail,  and  one  along  the 
front  edge  of  the  mirror.  The  angle  made  by  the  line  from  the  object  to 
the  mirror  with  the  front  of  the  mirror  bears  what  relation  to  the  angle 
made  by  the  line  to  your  eye  and  the  front  of  the  mirror?  Find  out  by 
comparing  these  angles  drawn  on  the  paper,  cutting  one  out  and  laying  it 
on  the  other. 

Can  you  write  thus? — 187.  Set  a  mirror  up  vertically  on  the  table. 
Lay  a  sheet  of  white  paper  in  front  of  it.  With  a  pencil  in  hand  place 
your  hand  on  the  paper.  Then  hold  a  card  in  your  left  hand  in  front  of 
your  face  so  that  you  cannot  see  your  hand  but  can  see  its  reflection  in  the 
mirror.  Write:  "I  see  the  image  of  my  hand,"  watching  the  formation 
of  the  letters  in  the  mirror.  Why  is  it  so  hard  to  do?  Who  can  learn  to 
do  it  in  the  shortest  time? 

Your  image  in  a  spoon. — 188.  Look  into  the  bowl  of  a  shiny  silver 
spoon  and  then  turn  it  over  and  look  on  the  back.  Can  you  see  why  your 
image  is  so  misshaped?  Draw  a  diagram  to  show  why.  You  may  use 
the  convex  and  concave  mirrors  furnished  in  the  laboratory  for  this  quite 
as  well  as  the  spoon. 


THE  CAMERA,  TELESCOPE,  MAGIC  LANTERN  83 

The  engine  headlight. — 189.  Hold  a  concave  mirror  in  the  sunlight 
and  see  at  what  distance  in  front  of  the  mirror  the  sun's  rays  are  brought 
to  a  point  by  the  mirror.  This  is  the  focal  point  of  the  mirror.  What  is 
the  focal  length  of  this  concave  mirror  in  inches?  If  a  candle  flame  is  set 
at  the  focal  point,  how  are  the  rays  of  light  reflected?  Try  the  experiment, 
holding  a  piece  of  white  paper  up  at  a  couple  of  feet  from  the  mirror  and 
catching  the  light  upon  it.  When  the  flame  is  moved  nearer  to  the  mirror, 
what  is  the  effect  on  the  beam  of  light?  Where  is  the  light  placed  with 
reference  to  the  focus  of  the  mirror  in  an  engine  or  automobile  headlight? 

The  magnifying  mirror. — -190.  Hold  a  concave  mirror  nearer  to  your 
eye  than  its  focal  length.  Look  at  your  eye  in  the  mirror.  Why  does  the 
dentist  use  a  concave  mirror  in  his  work? 

The  kaleidoscope. — 191.  Take  two  strips  of  mirror  about  i  inch  wide 
and  6  or  8  inches  long,  or  use  two  strips  of  glass,  one  side  of  each  of  whic^i 
is  covered  with  a  strip  of  black  paper  pasted  to  the  glass  along  the  edges. 
Cut  a  strip  of  dark  cardboard  or  blackened  wood  as  long  as  the^lass 
strips  and  sufficiently  wide  so  that  when  it  is  placed  between  tHe  long 
edges  of  the  mirrors  and  their  other  long  edges  are  in  contact  the 
faces  of  the  glass  strips  will  make  an  angle  of  30°.  Paste  dark  paper  over 
the  outside  of  this  so  that  it  will  be  held  together  and  form  a  triangular 
tube.  Cut  two  triangular  pieces  of  glass  of  sufficient  size  to  cover  the 
end  of  the  triangular  tube  and  place  between  them  along  their  edges 
some  narrow  strips  of  glass;  fill  the  space  between  them,  bounded  by 
this  edging,  with  broken  bits  of  colored  glass.  They  should  be  small  enough 
to  move  around  freely  between  the  glasses.  Bind  these  triangular  glasses 
together  and  fasten  them  to  one  end  of  the  triangular  tube  over  its  opening, 
pasting  black  paper  over  the  end  so  that  only  the  light  going  through  the 
opening  in  which  the  bits  of  colored  glass  are  will  enter  the  tube.  Look 
through  the  apparatus  now,  holding  the  end  containing  the,  colored  glass 
toward  the  light.  While  looking,  rotate  it  on  its  axis  so  that  the  bits  of 
glass  will  change  their  relative  positions.  Can  you  explain  what  you  see? 

Cameras. — To  make  a  pinhole  camera. — 192.  Cut  out  one  end  of  a 
pasteboard  box,  like  a  shoe  box.  Cover  the  hole  thus  made  with  paraffin 
paper  or  tracing  paper,  pasting  it  in  place.  With  a  pin  make  a  small  hole 
in  the  center  of  the  opposite  end  of  the  box.  Set  the  box  on  the  window 
sill,  pinhole  end  out;  throw  a  dark  cloth  over  the  inner  end  of  the  box  and 
at  the  same  time  over  your  head.  The  image  of  the  landscape  will  be  seen 
on  the  paraffin  paper.  (Draw  a  diagram  to  show  why.) 

193.  Cut  a  piece  of  blueprint  paper  the  size  of  the  end  of  the  box  on 
the  inside,  or  use  a  photographic  negative.  Fasten  either  by  means  of 
pins  inside  the  box  against  the  end  that  is  covered  with  tracing  paper, 


84  GUIDE  IN  PHYSICAL  NATURE-STUDY 

the  sensitive  side  of  paper  or  plate  toward  the  pinhole.  Blueprint  paper 
must  be  handled  in  dim  light  and  the  photographic  negative  must  be  put 
in  place  in  a  dark  room  lighted  by  a  red  light  (see  below).  The  pinhole 
camera  may  be  set  on  the  window  sill  on  a  bright  day  and  left  for  a  half- 
hour  if  the  blueprint  paper  is  taken,  for  five  minutes  if  the  negative  is 
used.  Then  the  blueprint  paper  may  be  washed,  or  the  negative  developed 
(see  below),  and  the  image  of  the  outdoor  scene  will  appear. 

The  camera  obscura. — 194.  A  camera  for  sketching  may  be  made  by  using 
a  larger  wooden  box  with  one  side  off.  Set  the  box  on  the  table  in  front 
of  the  open  window,  the  open  side  toward  you.  In  the  middle  of  the  side 
away  from  you,  8  inches  or  so  from  the  top  of  the  box,  bore  a  small  hole. 
Fasten  a  mirror  to  the  top  of  the  box  opposite  this  hole  and  a  foot  from  it, 
so  that  the  light  will  be  reflected  down  to  the  bottom  of  the  box.  Throw  a 
dark  cloth  over  the  open  side  of  the  box  and  put  your  head  under  the  cloth. 
Place  a  white  paper  on  the  bottom  of  the  box.  The  image  of  the  out-of- 
door  scene  is  thrown  on  this  white  paper  and  may  be  sketched  in  outline. 

The  lens  camera. — So  little  light  comes  in  through  the  pinhole  in  the 
camera  above  that  it  takes  a  very  long  exposure  to  affect  the  sensitive 
plate.  195.  If  the  hole  is  made  larger,  the  image  is  blurred.  (Show  by 
a  diagram  why  this  is  so.)  But  if  a  lens  is  set  in  the  opening  a  clear  image 
may  be  obtained,  even  with  a  wide  opening. 

To  make  a  lens. — 196.  Smear  a  little  vaseline  on  the  edges  of  two 
watch  crystals.  Be  careful  not  to  get  the  vaseline  on  the  outside.  Put 
these  under  water  and  bring  them  together  accurately,  edge  to  edge. 
Hold  them  firmly  together  with  the  left  thumb  and  fingers  and  bring  them 
out  of  water.  The  vaseline  prevents  the  water  running  out.  Dry  them 
off,  particularly  the  edges,  and  bind  the  edge  of  this  "lens"  with  surgeons' 
tape,  seeing  that  it  adheres  closely  so  that  the  water  will  not  escape.  You 
have  thus  a  double  convex  lens. 

Images  formed  by  the  lens. — 197.  Hold  the  lens  up  in  the  right  hand 
in  front  of  a  sheet  of  white  paper  tacked  up  in  a  darkened  room,  and  in 
the  left  hand  hold  a  candle.  Move  the  lens  nearer  to  the  candle  or  to 
the  paper,  as  may  be  necessary,  to  throw  a  clear  image  of  the  candle  flame 
on  the  paper  screen.  Note  the  size  of  the  image.  Measure  the  distance 
from  the  paper  to  the  lens  and  from  the  lens  to  the  candle.  Set  the  lens 
twice  as  far  from  the  screen  and  move  the  candle  back  and  forth  until  the 
image  is  clear  again.  Is  the  candle  nearer  to  the  lens  or  farther  from  it 
than  before?  Repeat  the  experiment,  setting  the  lens  half  as  far  from  the 
screen  as  in  the  first  case.  Is  the  image  smaller  or  larger? 

The  nearer  the  object  is  to  a  convex  lens,  the the  screen 

must  be  from  the  lens  to  get  the  clear  image  and  the the 


THE  CAMERA,  TELESCOPE,  MAGIC  LANTERN  85 

image  is.  You  will  see  then  why,  in  the  ordinary  cameras,  the  lens  is 
mounted  so  that  its  distance  to  the  sensitive  plate  may  be  altered  in  order 
to  focus  the  image  sharply. 

The  lens  as  a  burning  glass. — 198.  Hold  the  lens  in  the  sunlight  so 
that  the  light  will  shine  through  it.  Focus  the  light  in  a  tiny  point  on  a 
sheet  of  white  paper.  Not  only  is  the  light  focused  but  the  heat  also,  and 
the  paper  may  be  set  on  fire.  Measure  the  distance  from  the  lens  to  the 
paper  when  the  point  of  light  is  as  small  as  you  can  get  it.  This  is  the 
focal  length  of  the  lens. 

The  camera. — 199.  Enlarge  the  pinhole  in  the  pinhole  camera  so  that 
the  lens  can  be  set  in  the  hole.  Fasten  it  in  with  dark  paper  pasted  around 
the  opening  and  on  the  lens.  Make  a  wooden  frame  that  fits  snugly  as 
it  stands  up  in  the  inside  of  the  box.  Remove  the  tracing  paper  from  the 
back  of  the  box  and  fasten  it  to  the  front  of  the  frame.  Set  the  frame  in 
the  box  back  of  the  lens,  about  as  far  from  it  as  the  focal  length  of  the  lens. 
Set  the  camera  on  the  window  and  cover  the  open  end  with  the  dark  cloth, 
covering  your  head  also.  Look  on  the  paraffin  paper  for  the  image  of  the 
objects  out  of  doors.  If  the  image  is  not  clear,  move  the  frame  back  and 
forth  until  it  is  reasonably  clear.  Load  the  camera  as  before  with  a  sensi- 
tive plate,  keeping  the  lens  covered  until  the  exposure  is  made.  The 
exposure  now  may  be  short,  a  second  or  two,  to  get  a  good  negative. 

Camera  plates. — 200.  Examine  a  sensitive  plate  in  the  light.  Take  it 
out  of  the  box  in  the  dark  room  (see  below)  and  close  the  box  before  opening 
the  door.  Note  that  one  surface  of  the  plate  is  covered  with  a  gelatine 
film  in  which  are  held  certain  substances  sensitive  to  light.  These  are 
salts  of  silver.  When  light  acts  on  silver  salts  they  often  break  down, 
depositing  grains  of  metallic  silver  that  look  black  in  the  mass. 

201.  Take  a  crystal  or  two  of  silver  nitrate  and  dissolve  in  a  test  tube 
in  a  tablespoonf ul  of  hot  water.  Dip  a  piece  of  filter  paper  or  white  blotting 
paper  in  this  and  place  it  in  strong  sunlight.  The  paper  darkens  as  the  silver 
is  deposited. 

The  dark  room. — -Sensitive  plates  and  print  papers  must  be  handled 
in  a  room  lighted  by  red  light  that  does  not  act  at  all  rapidly  on  the  sen- 
sitive surface.  202.  To  make  a  safe  dark-room  light,  a  sheet  of  red 
tissue  paper,  doubly  thick,  may  be  tied  over  the  electric  light,  or  a  lighted 
candle  may  be  set  in  a  shoe  box,  one  side  of  which  has  been  cut  out  and 
the  opening  covered  with  red  tissue  paper.  Punch  holes  near  the  bottom 
and  in  the  top  of  the  box  for  ventilation  and  screen  these  also  with  red 
paper. 

To  develop  the  plate. — A  plate  exposed  in  a  camera  does  not  show  the 
image  when  removed,  for  the  light  has  acted  for  so  short  a  time  that  the 


86  GUIDE  IN  PHYSICAL  NATURE-STUDY 

process  of  disintegration  of  the  silver  salts  has  only  just  begun.  It  is 
completed  by  "developing."  203.  At  some  photo  supply  store  buy  a 
package  of  hydrochinone  developing  powders  (six  for  twenty-five  cents), 
and  a  half-pound  of  acid  fixer.  Dissolve  the  fixer  in  one  quart  of  water 
and  put  it  in  a  pan  in  the  dark  room.  Dissolve  one  of  the  powders  in 
4  ounces  of  water,  dissolving  the  content  of  the  blue  paper  first,  then  adding 
that  of  the  pink.  Put  this  in  a  small  pan  or  a  soup  plate  in  the  dark  room. 
Remove  the  exposed  sensitive  plate  from  the  camera  in  the  dark  room. 
Handle  it  by  its  edges.  Dip  it  in  water,  then  put  it  in  the  developer, 
sensitive  side  up,  promptly  wiping  off  its  face  with  a  bit  of  absorbent 
cotton  wet  in  the  developer,  and  see  that  the  whole  face  is  covered 
instantly  with  the  developer.  Rock  the  pan  or  plate  so  that  the 
developer  will  move  about  in  the  pan.  The  image  should  appear  in  a  few 
seconds.  When  it  begins  to  show  through  on  the  back  of  the  plate,  take 
the  plate  out  of  the  developer  and  put  it  in  the  fixer,  face  up.  Leave  it  in  for 
ten  minutes,  or  until  all  the  white  has  disappeared  from  it.  Then  wash  it 
in  running  water  for  thirty  minutes  or  put  it  through  a  dozen  changes  of 
water,  leaving  it  in  each  for  two  or  three  minutes.  Set  it  up  on  edge  to  dry. 

The  negative. — This  gives  a  negative,  so  called  because  all  light  areas 
in  the  object  before  the  camera  are  dark  in  the  negative  and  all  dark  areas 
are  light.  The  negative  is  used  to  make  the  picture. 

Printing. — 204.  In  the  dark  room  place  a  sheet  of  print  paper  like 
"Cyko"  or  "Solio,"  of  the  same  size  as  the  negative  with  its  sensitive 
face  against  the  film  side  of  the  negative.  Cover  the  back  of  the  paper 
with  a  piece  of  cardboard  or  wood  (or  the  back  of  the  printing  frame). 
Expose  the  paper  to  the  light  by  letting  the  light  fall  on  the  negative.  At 
6  feet  from  a  sixteen-candle-power  electric  light  an  exposure  of  three  to 
six  seconds  is  enough  for  a  negative  of  ordinary  density.  The  print  is 
developed  like  a  plate,  using  8  ounces  of  water  for  a  package  of  developer, 
and  metol  developer  is  better  than  hydrochinone  for  this.  It  is  fixed  in  the 
fixing  bath,  washed  and  dried  as  was  the  plate. 

The  good  camera. — 205.  Hold  a  lens,  such  as  we  have  made,  up  to 
the  light  and  look  through  it  at  some  object,  like  the  window.  It  will  be 
noticed  that  the  image  is  more  or  less  distorted,  straight  lines  appearing 
curved,  and  the  image  is  surrounded  by  more  or  less  of  a  halo  of  color. 
These  defects  of  a  lens  are  in  part  overcome  by  using  only  the  central 
portion  of  the  lens;  hence  a  lens  is  usually  "diaphragmed  down"  in  a  camera. 
Examine  a  good  camera  to  see  its  parts — lens,  diaphragm,  bellows,  rack- 
and-pinion  focusing  adjustment,  ground-glass  back,  plate  holders,  etc. 

Refraction. — 206.  Put  a  coin  in  a  cup  or  bowl  which  sets  on  the 
table.  Stand  back  from  the  table  so  that  you  can  just  see  the  coin  on  the 


THE  CAMERA,  TELESCOPE,  MAGIC  LANTERN  87 

bottom  over  the  edge  of  the  bowl.  Step  back  one  step  farther,  until  the 
coin  is  no  longer  seen.  Have  someone  pour  water  into  the  bowl  slowly 
so  as  not  to  disturb  the  coin.  What  happens?  Evidently  the  ray  of  light 
from  the  coin  going  over  the  edge  of  the  bowl,  a  ray  that  would  go  over 
your  eye,  is  bent  down  by  the  water  to  your  eye.  207.  Hold  a  prism  of 
glass  in  your  hand,  the  base  of  the  triangle  down  and  horizontal,  the  edge 
up,  and  look  at  a  lighted  candle  on  the  table.  Trace  the  course  of  the  ray 
of  light.  Draw  a  diagram  of  it.  As  the  ray  enters  the  glass  is  it  bent 
toward  or  away  from  the  line  that  is  perpendicular  to  the  surface  at  this 
point?  As  the  ray  comes  out  of  the  glass  or  water,  how  is  it  bent  with 
reference  to  the  perpendicular?  It  is  this  refraction  of  the  light,  passing 
through  a  lens,  that  makes  it  form  an  image.  208.  Diagram  the  forma- 
tion of  an  image  by  a  lens. 

To  make  a  telescope. — 209.  Wrap  several  thicknesses  of  stiff  paper 
blackened  on  one  side,  black  face  in,  on  the  outside  of  a  cylindrical  stick 
of  wood  and  paste  down  the  edges  so  as  to  make  a  paper  tube,  black  inside, 
when  it  is  slipped  off  the  stick  of  wood.  Make  another  similar  loose  tube 
on  the  outside  of  this  so  that  they  will  telescope  into  each  other.  Fasten 
one  of  the  homemade  lenses  or  a  plane  convex  glass  lens  on  the  end  of  the 
larger  tube.  This  will  be  the  objective  of  the  telescope.  Have  this  tube 
about  as  long  as  the  focal  length  of  the  lens  used.  Fasten  another  lens, 
the  eyepiece,  on  one  end  of  the  smaller  tube  and  let  this  tube  be  two- 
thirds  as  long  as  the  longer  one.  Cut  a  circular  hole  of  about  f-inch  dia- 
meter in  a  piece  of  black  paper  and  fasten  this  over  the  eyepiece  so  as  to 
cover  all  but  its  central  portion.  Slip  the  open  end  of  the  short  tube  into 
the  open  end  of  the  larger  tube.  Look  through  the  eyepiece,  shoving  the 
small  tube  in  or  out  until  you  see  the  outdoor  object.  The  image  formed 
by  the  objective  is  examined  by  the  eye  looking  through  the  eyepiece. 
The  tubes  are  really  unessential.  You  may  hold  two  lenses,  one  in  each 
hand,  and  looking  through  both  held  in  line  with  the  eye  change  their 
relative  position  so  as  to  get  the  telescope  effect. 

Magnifier  and  microscope. — -210.  The  homemade  double  convex  lens 
can  be  used  as  a  simple  magnifier.  Try  it.  Must  the  object  to  be  magni- 
fied be  nearer  to  the  lens  or  farther  from  it  than  its  focal  length  when  it  is 
seen  enlarged? 

211.  To  make  the  compound  microscope,  proceed  as  in  making  the 
telescope,  only  make  the  larger  tube  three  tunes  as  long  as  the  focal  length 
of  the  lens.  The  object  to  be  seen  must  be  an  inch  or  so  from  the  objective 
and  in  strong  light.  Move  the  eyepiece  up  or  down  until  the  magnified 
object  is  seen. 


88  GUIDE  IN  PHYSICAL  NATURE-STUDY 

To  make  the  magic  lantern. — 212.  Use  the  homemade  camera  for  the 
body  of  the  lantern.  Set  it  horizontally  on  the  table.  Fasten  an  electric 
light  inside  the  box  so  that  it  is  about  as  far  from  the  lens  as  the  focal 
length  of  the  latter.  This  lens  now  serves  as  a  condenser.  With  India 
ink  draw  a  picture  on  a  piece  of  glass  or  on  tracing  paper.  Fasten  this  up 
in  front  of  the  condenser.  Hold  another  homemade  lens  an  inch  or  so  in 
front  of  the  picture.  Move  a  sheet  of  white  paper,  held  a  few  feet  in  front 
of  the  lens,  nearer  to  and  farther  from  the  lens  until  the  image  of  the  picture 
appears  on  the  paper.  A  block  of  wood  with  a  hole  bored  in  it  with  a 
large  auger,  opposite  the  condenser,  may  be  set  on  the  table  to  serve  as  a 
slide  carrier  for  magic-lantern  slides.  The  objective  lens  may  also  be 
mounted  on  a  similar  block  and  the  magic  lantern  may  be  set  up  at  any 
time  for  use.  Much  better  results  can  be  obtained  if  well-ground  glass 
lenses  are  used  in  place  of  our  homemade  lenses,  but  the  latter  will  show 
the  method  of  construction. 

The  rainbow. — 213.  Look  through  the  prism  at  some  well-lighted 
object,  like  the  window  sill,  and  note  that  the  rays  of  white  light  are 
evidently  broken  up  or  dispersed  into  their  component  colors.  It  is  this 
dispersion  of  sunlight  as  it  passes  through  the  raindrops  that  produces 
the  rainbow.  214.  Let  a  beam  of  light  into  a  darkened  room  through  a 
slot  in  the  shutter  or  in  a  board  set  below  the  curtain  and  set  the  prism 
just  inside  the  slot  so  that  the  beam  of  light  passes  through  it.  The  band 
of  color  will  be  seen  on  walls  or  ceiling.  , 

Mixing  colors. — The  reverse  of  this  is  true,  that  colors  may  be  blended 
to  produce  new  ones,  even  to  produce  white.  Send  for  a  sample  book  of 
educational  colored  papers  (Thomas  Charles  and  Co.,  2249  Calumet  Ave., 
Chicago).  215.  Cut  two  circular  pieces  of  paper  from  these  samples, 
one  blue  and  one  yellow.  Slit  each  disk  from  its  margin  to  its  center. 
Slip  the  edge  of  one  of  these  cuts  into  the  other  and  adjust  the  two  disks 
so  that  about  half  of  each  disk  shows  its  color.  Punch  a  hole  in  the  middle 
of  the  disks  and  slip  them  on  the  stem  of  the  peg  top  (p.  43).  Punch  a 
hole  in  the  center  of  a  slice  of  a  small  cork  and  slip  this  on  the  stem  to  hold 
the  papers  in  place.  Spin  the  tip  and  note  the  color.  Change  the  relative 
amounts  of  color  exposed,  letting  one  blue  disk  show  two-thirds  and  the 
yellow  one- third.  Spin  again  and  note  the  results.  216.  Add  a  third  disk 
of  white  paper,  exposing  one- third  of  each  disk,  blue,  yellow,  and  white. 
What  is  the  effect  when  the  top  is  spun?  217.  Try  disks  of  white  and 
black  paper,  each  half-exposed.  Try  disks  of  red  and  yellow,  or  red  and 
green.  218.  Can  you  recombine  by  means  of  the  top  the  rainbow  colors 
(violet,  indigo,  blue,  green,  yellow,  orange,  red)  to  make  white?  How 
would  the  color  top  be  useful  in  mixing  paints? 


THE  CAMERA,  TELESCOPE,  MAGIC  LANTERN  89 

Optical  illusions. — There  are  many  interesting  optical  illusions  that 
show  that  you  do  not  always  see  what  you  think  you  see.  219.  Draw 
two  parallel  lines  i^  inches  apart  and  6  inches  long.  At  intervals  of  a 
half-inch  on  each  line  draw  half -inch  lines  into  the  space  between  the  lines, 
these  short  lines  all  pointing  one  way  and  standing  at  an  angle  of  45°  to 
the  parallel  lines.  Do  the  long  lines  still  appear  parallel? 

220.  Draw  two  inch  squares  near  together,  one  of  light  lines,  one  of 
heavy.     Draw  two  half-inch  squares  inside  the  inch  squares,  their  sides 
separated  from  those  of  the  larger  squares  by  half-inch  spaces.     Make 
the  inner  square  of  heavy  lines  in  the  larger  square  of  light  lines,  and  vice 
versa.    Connect  each  corner  of  the  inner  square  to  the  adjacent  corner  of 
the  outer  square.    How  do  the  resulting  figures  compare? 

221.  Draw  two  lines  a  few  inches  apart,  one  i  inch  long,  the  other  4^ 
inches  long.    In  the  middle  of  each  mark  off  by  short  cross-lines  ^  inch. 
Do  the  marked-off  portions  look  equal?    On  the  same  paper  several  inches 
apart  draw  two  lines  each  2  inches  long.    At  the  end  of  each  line  draw  two 
half-inch  lines  making  a  V,  its  point  coincident  with  the  end  of  the  line. 
Let  the  open  ends  of  the  V  on  one  line  be  toward  each  other,  on  the  other 
away  from  each  other.    Do  the  two  2-inch  lines  appear  now  of  equal 
length? 


THE  HOMEMADE  ORCHESTRA 

A  ukelele. — 222.  Cut  a  2-inch  square  hole  in  the  middle  of  the  cover 
of  a  cigar  box.  Cut  a  strip  of  f-inch  pine  2  inches  wide  and  18  inches 
long.  In  one  end  of  this  saw  out  two  slots  the  long  way  of  the  strip,  each 
f  inch  wide  and  2  inches  long  and  f  inch  from  the  edge  of  the  strip.  Through 
the  walls  of  each  of  these  slots  and  at  right  angles  to  them  bore  J-inch 
holes  about  i  inch  apart.  Have  those  on  one  slot  alternate  with  those  on 
the  other.  Cut  out  four  round  pegs  i^  inches  long  with  flat  heads  like 
those  on  the  violin,  so  that  the  pegs  will  fit  these  holes  tightly.  With  an 
awl  make  a  hole  in  the  middle  of  each  peg.  Nail  the  other  end  of  this 
long  strip  on  the  middle  of  one  end  of  the  cigar  box,  the  face  of  the  strip 
flush  with  the  top  of  the  box.  Fasten  four  wires,  about  Nos.  32,  28,  24, 
1 8,  by  tacks  to  the  end  of  the  cigar  box  opposite  the  long  strip  to  serve 
as  strings.  Tack  a  piece  of  thin  wood  to  serve  as  a  bridge  on  the  cover  of 
the  box  below  the  hole  and  parallel  to  its  lower  edge.  Pass  a  string  over 
the  bridge,  making  a  little  notch  in  the  top  edge  of  the  bridge  to  hold  it 
and  put  the  free  end  of  the  wire  through  the  hole  in  a  peg.  Turn  the  peg  so 
as  to  wind  the  wire  about  it  and  tighten  the  string.  Do  the  same  for  the 
other  strings.  Tighten  the  strings  so  that  they  will  sound  do,  mi,  sol,  do 
on  the  scale.  Can  you  play  a  tune? 

Banjo. — 223.  Make  a  similar  instrument,  using  a  round  cheese  box  in 
place  of  the  cigar  box.  A  string  band  might  easily  be  improvised  if  boxes 
of  various  sizes  are  used  to  make  the  instruments  and  these  are  tuned  so 
as  to  be  in  harmony.  The  larger  instruments  could  be  tuned  an  octave  or 
two  lower  than  the  small  ones. 

Why  some  strings  on  the  piano  are  long  and  coarse. — 224.  Fasten  two 
tacks  3  or  4  inches  apart  in  one  end  of  the  table  or  in  one  end  of  a  board 
as  long  as  the  desk.  Tie  the  ends  of  strings,  one  coarse  and  one  fine,  each 
to  one  of  these  two  tacks.  Make  two  bridges  and  set  one  near  each 
end  of  the  table  or  board  so  that  the  strings  can  pass  over  them.  Hang 
equal  weights  of  a  pound  or  two  to  each  string.  Pluck  the  strings  so.  that 
they  will  sound  a  note.  What  do  you  learn?  Double  the  weight-  on  each 
string  and  pluck  the  strings  again.  What  additional  fact  can  you  record? 
Move  the  bridges  closer  together  and  then  pluck  the  strings.  Record  the 

results.    The  coarser  the  string,  the the  note  it  gives  off. 

The  longer  the  string,  the the  note  omitted.     The  greater  the 

tension  of  the  string,  the the  note  it  gives. 

90 


THE  HOMEMADE  ORCHESTRA  91 

Why  the  violin  has  a  box. — 225.  Set  a  large  cigar  box  with  a  hole  cut 
in  its  lid  under  the  strings  on  the  table  and  put  the  bridges  on  its  top,  one 
at  either  end,  setting  the  two  strings  over  them.  Then  pluck  the  strings. 
How  does  the  sound  compare  with  that  given  off  when  the  cigar  box  is 
not  used  but  the  bridges  are  set  at  the  same  distance  on  the  table  top  or 
board?  The  thin  wood  of  the  box  also  is  set  in  vibration  as  well  as  the 
air  in  the 'box.  226.  Roll  up  some  stiff  paper  to  make  a  flaring  conical 
trumpet.  Talk  into  the  small  end.  Why  is  the  sound  of  your  voice 
so  loud?  227.  Hold  your  nose  shut  and  then  talk.  You  change  the 
character  of  the  sound  by  cutting  off  certain  resonance  chambers.  How 
can  you  change  the  pitch  of  the  note  given  off  by  a  stretched  string?  The 
intensity  of  the  sound?  The  quality? 

To  make  a  whistle. — 228".  Cut  an  8-inch  length  of  good-sized  bamboo 
open  at  both  ends.  Fit  a  cork  plunger  at  one  end,  on  the  end  of  a 
stick,  as  if  making  a  squirt  gun  (p.  52).  Cut  a  transverse  notch  i  inch 
from  the  other  end,  a  third  of  the  way  through  the  bamboo,  the  edge  of 
the  notch  toward  the  near  end,  inclined  to  the  long  axis  of  the  bamboo 
about  45°,  the  other  edge  vertical  to  this  long  axis.  Cut  off  the  end  of  the 
bamboo  near  the  notch  parallel  to  the  adjacent  edge  of  the  notch,  i.e., 
at  an  angle  of  45°.  Plug  this  end  of  the  bamboo  down  to  the  notch  with 
a  cork,  cut  off  to  conform  to  the  inclination  of  the  end.  On  the  side  of 
the  cork  where  the  notch  is,  cut  off  a  thin  slice  so  as  to  make  a  slot  through 
which  to  blow.  When  blowing  through  this  the  whistle  should  operate 
and  the  note  may  be  changed  by  pushing  in  or  drawing  out  the  plunger. 
This  instrument  may  be  added  to  the  orchestra. 

Sound  due  to  vibrations  set  up  by  the  sounding  body.  229.  Fold  an 
inch  strip  of  light-weight  paper  in  half  so  as  to  make  a  little  rider.  Drop 
it  on  the  middle  of  a  stretched  string  that  is  emitting  a  sound.  What 
happens  and  what  does  it  show?  Set  a  bell  to  ringing  and  bring  a  pith  ball 
suspended  by  a  fine  string  against  its  edge.  What  happens  and  why? 

230.  Draw  the  edge  of  a  piece  of  stiff  card,  like  a  post  card,  held 
between  thumb  and  finger,  over  the  teeth  of  a  comb.  Can  you  feel  the 
vibrations?  Draw  it  over  rapidly,  then  very  rapidly.  The  more  frequent 
the  vibrations,  the the  pitch  of  the  note  emitted. 

In  the  whistle  it  is  the  column  of  air  that  is  made  to  vibrate.  The 

shorter  the  vibrating  column,  the the  pitch  of  the  note. 

From  which  pipes  do  the  bass  notes  of  the  pipe  organ  come? 

A  rattler. — -231.  From  the  wood  of  a  cigar  box  cut  two  strips  6  by  ij 
inches.  Cut  a  block  of  f-inch  stuff  ij  inches  wide  and  J  inch  longer  than 
an  empty  spool.  With  brads  fasten  the  two  strips  to  the  equally  wide 
ends  of  the  block  so  that  they  are  parallel  to  each  other,  the  block  between 


92  GUIDE  IN  PHYSICAL  NATURE-STUDY 

them.  Cut  another  6-inch  strip  just  wide  enough  to  fasten  on  the  block 
and  the  first  two  strips  with  brads,  and  so  close  one  side  of  this  long  box, 
the  other  side  and  one  end  of  which  are  still  open.  Cut  a  piece  of  wood 
about  i  inch  square  and  6  inches  long  to  serve  as  a  handle.  Whittle  down 
2  inches  at  one  end  of  this  so  that  it  will  fit  tightly  into  the  hole  of  the 
spool,  but  do  not  put  the  spool  on  yet.  Cut  deep  notches  in  the  ends  of 
the  spool  so  as  to  make  the  ends  toothed  all  around.  Bore  two  holes 
slightly  larger  than  the  hole  in  the  spool,  one  in  each  of  the  ij-inch-wide 
strips  about  f  inch  from  the  ends  opposite  the  blocks.  Place  these  holes 
near  enough  to  the  uncovered  side  of  the  box  so  that  when  the  round  end 
of  the  handle  that  carries  the  spool  is  put  through  them  the  teeth  on  the 
spool  ends  will  project  above  the  edges  of  the  adjacent  strips.  Put  the 
round  end  of  the  handle  through  one  hole,  then  force  it  through  the  hole 
in  the  spool  far  enough  to  stick  through  the  second  hole.  Cut  a  strip  of 
real  thin  wood  as  a  tongue,  making  it  as  wide  as  the  spool  and  long  enough 
so  that  when  one  end  is  fastened  by  brads  to  the  block  the  other  will  press 
against  the  teeth  of  the  spool. 

While  holding  the  handle  in  your  hand  rotate  the  hand  so  as  to  whirl 
the  box  about  the  handle.  The  teeth  on  the  spool  lift  the  tongue  and  drop 
it  repeatedly  with  incessant  clatter.  If  the  piece  of  wood  used  for  the 
tongue  is  too  stiff  to  spring  up  as  the  teeth  lift  it  file  or  sandpaper  the  base 
away  near  the  attachment  to  the  block  until  it  is  springy.  This  may  not 
be  a  very  musical  instrument  to  add  to  the  orchestra,  but  it  does  show 
well  that  sound  is  produced  by  the  vibration  of  the  sounding  body,  in  this 
case  the  tongue  of  the  rattler.  The  box  serves  as  a  resonator  to  increase 
the  volume  of  sound. 

The  triangle. — 232.  Bend  an  i8-inch-long  piece  of  J-inch  round  iron 
or  very  heavy  wire  into  the  shape  of  an  equilateral  triangle,  the  ends  of 
the  wire  not  quite  touching.  Hang  this  on  a  string  by  one  angle  and  play 
it  by  tapping  it  with  a  large  nail. 


HOW  TO  MAKE  THE  PHONOGRAPH  AND  TELEPHONE 

The  phonograph. — 233.  In  the  making  of  a  phonograph  record  a  sharp 
stylus  borne  on  a  thin  disk  at  the  small  end  of  a  receiver  horn  makes  a  series 
of  impressions  in  a  spiral  line  on  a  rotating  plastic  plate  as  the  disk  is 
caused  to  vibrate  by  the  sound  waves  entering  the  horn  when  the  per- 
former sings  or  speaks  into  it.  This  wax  plate  is  then  used  as  a  pattern  to 
mold  hard-rubber  plates,  exact  duplicates  of  itself,  and  these  are  the  records. 
When  the  sharp  needle  of  the  phonograph  travels  over  the  line  of  little 
hills  and  valleys  it  causes  the  disk  to  which  it  is  attached  to  vibrate  and 
reproduce  the  same  succession  of  sound  waves  that  caused  the  impression 
on  the  original  plate. 

When  one  understands  the  principle  in  accord  with  which  the  phono- 
graph works  it  is  not  difficult  to  make  one  that  will  operate  fairly  well. 
Use  a  planed  board  9  by  1 2  inches  as  the  base.  Draw  a  line  down  through 
its  center.  One  inch  from  one  end  of  this  line  bore  a  hole  large  enough  to 
take  a  hardwood  upright  peg  that  will  fit  the  hole  of  a  spool,  so  that  the 
latter  can  revolve  on  the  peg  smoothly.  Let  the  peg  be  long  enough  to 
project  slightly  above  the  end  of  the  spool  when  the  lower  end  of  the  peg 
is  set  securely  in  the  hole  in  the  baseboard.  Sharpen  off  the  top  of  the  peg 
to  a  blunt  point. 

The  turntables. — Cut  a  lo-inch  square  of  J-inch  board  that  is  perfectly 
flat  and  draw  upon  it  the  diagonals  of  the  square  so  as  to  find  its  center. 
At  this  point  make  a  depression  into  which  the  upper  end  of  the  peg  may 
fit.  Fasten  the  spool  on  this  same  side  of  the  board,  its  hole  directly  over 
the  hole  on  the  board.  The  square  board  on  the  spool  will  revolve  on  the 
peg.  On  the  top  of  this  board  at  its  center  glue  a  short  round  peg,  just 
large  enough  to  fit  the  hole  in  the  record  to  be  used.  If  it  tends  to  slip, 
the  record  may  be  fastened  in  place  by  thumb  tacks  placed  so  as  to  lap 
over  its  edge. 

Place  the  baseboard  on  the  table  in  front  of  you  so  that  the  turntable 
is  at  its  distant  end.  Then  at  the  left-hand  corner  near  you  draw  a  square 
with  i-inch  sides,  the  corner  of  the  board  being  one  corner  of  the  square. 
By  means  of  a  nail  driven  into  the  corner  of  this  square  opposite  the  corner 
of  the  baseboard  fasten  a  wheel  not  exceeding  9  inches  in  diameter.  This 
may  be  a  wheel  taken  from  an  old  rubber- tired  doll  carriage  or  a  cart,  the 
rubber  tire  removed  so  that  the  rim  is  grooved,  or  it  may  be  a  wheel  cut 
out  of  J-inch  board,  the  edge  grooved  with  a  round  file.  Near  the  rim  of 

93 


94  GUIDE  IN  PHYSICAL  NATURE-STUDY 

this  wheel  fasten  a  handle  so  that  it  may  be  revolved  horizontally.  Tie  a 
heavy  cord  or  long  leather  shoe  lace  about  the  rim  of  this  wheel  and  the 
spool  under  the  turntable  so  that  it  will  serve  as  a  belt. 

The  vibrating  disk  and  the  arm  that  carries  it. — Take  a  small  tin  or  glass 
funnel  the  mouth  of  which  is  not  over  2  inches  in  diameter.  Cut  a  circular 
piece  of  mica,  split  very  thin,  the  same  size  as  the  mouth  of  the  funnel  and 
glue  its  edge  to  the  rim  of  the  funnel's  mouth  all  round.  At  the  center 
of  this  mica  disk  glue  a  small  piece  of  cork  large  enough  to  hold  the  butt 
end  of  the  stylus,  usually  used  on  the  phonograph,  or  the  end  of  a  machine 
needle  broken  in  half. 

Cut  a  strip  of  J-inch  pine  i  inch  wide  and  1 2  inches  long.  A  half- 
inch  from  one  end  bore  a  hole  large  enough  to  take  the  stem  of  the  funnel; 
at  the  other  end,  one  to  take  a  long  brad.  Two  inches  from  the  end  where 
the  funnel  goes  cut  the  strip  square  across  and  refasten  the  cut-off  portion 
to  the  long  part  by  a  hinge  set  on  the  i -inch- wide  side  of  both.  Put  a  bit 
of  rubber  tube  or  a  rubber  washer  on  the  stem  of  the  funnel  close  to  the 
flare.  Set  the  stem  of  the  funnel  into  the  hole  of  the  wood  strip,  its  tip 
protruding  on  the  same  side  to  which  the  hinge  is  affixed.  Slip  a  6-inch 
length  of  rubber  tubing  on  the  stem  of  the  funnel  and  push  it  down  until 
the  end  is  pressed  against  the  wood  strip. 

A  piece  of  |-inch  wood  2  inches  wide  is  to  be  fastened  as  an  upright  to 
the  end  of  the  baseboard,  its  edge  ij  inches  from  the  corner  opposite  the 
wheel.  It  must  be  sufficiently  long  so  that  when  the  arm  bearing  the  funnel 
is  attached  to  its  top  by  the  long  brad  in  a  horizontal  position  the  tip  of 
the  stylus  will  rest  on  the  record.  After  this  upright  and  the  arm  are  in 
place  an  additional  support  for  the  arm  is  rigged  so  that  the  stylus  may  not 
bear  too  heavily  on  the  record.  Bend  a  stiff  wire  into  a  2-inch-wide  U 
with  sides  long  enough  to  straddle  the  arm,  the  curve  of  the  U  several 
inches  above  the  arm.  Shove  the  tips  of  the  U  down  into  holes  bored  in 
the  baseboard  2  inches  apart.  Dent  the  top  of  the  U  and  fasten  a  loop 
of  string  from  the  dent  to  the  arm  so  as  to  hold  it  up  and  still  leave  it 
free  to  swing  from  side  to  side. 

The  horn. — Roll  a  piece  of  stiff  paper  into  the  form  of  a  good-sized  horn. 
Glue  it  so  that  it  will  stay  in  shape.  Glue  into  its  small  end  a  cork  through 
the  center  of  which  runs  a  short  length  of  glass  tubing.  On  this  slip  the 
end  of  the  rubber  tube,  which  also  attaches  to  the  funnel.  On  the  side  of 
the  base  fasten  an  upright  on  top  of  which  is  fixed  a  small  hoop  to  hold 
the  horn. 

When  the  record  is  placed  on  the  turntable  the  tip  of  the  stylus  in  its 
outermost  groove  must  be  rotated  very  steadily  by  the  wheel  in  the  direction 
opposite  to  that  in  which  the  hands  of  a  clock  move.  The  proper  speed 


HOW  TO  MAKE  THE  PHONOGRAPH  AND  TELEPHONE        95 

of  rotation  will  have  to  be  determined  by  trial  until  the  reproduction 
sounds  natural. 

Pan's  pipes. — 234.  Cut  glass  tubing  with  about  J-inch  bore  so  as  to 
make  eight  pieces  3^,  3!,  4,  4j,  4!,  5},  sJ,  and  6}  inches  long.  Plug  one 
end  of  each  with  a  cork  plug  J  inch  long  set  in  flush  with  the  end.  Fasten 
these  pipes  to  a  block  of  wood,  their  open  ends  at  the  "same  level  and  far 
enough  apart  so  that  you  can  blow  across  the  end  of  each  to  produce  a 
note.  They  should  give  the  successive  notes  of  an  octave. 

The  flute. — 235.  Take  one  joint  of  bamboo  as  long  as  is  obtainable, 
with  one  end  closed,  the  other  open.  Near  the  closed  end  bore  a  hole  on 
one  side  about  J  inch  in  diameter.  Blow  across  this  to  get  a  tone.  Measure 
the  distance  from  this  hole  to  the  open  end.  Bore  another  hole  on  the  same 
side  one-half  of  the  distance  from  the  mouth  hole  to  the  open  end.  Locate 
the  other  holes  in  a  row  on  the  same  side,  nine-eighths  of  the  distance  from 
the  mouth  hole  to  this  central  hole,  five-fourths,  four-thirds,  three-halves, 
five-thirds,  fifteen-eighths,  respectively.  You  now  have  another  instrument 
for  the  orchestra.  To  play  it  hold  the  thumbs  on  the  side  of  the  flute  opposite 
the  holes,  the  first,  second,  and  third  fingers  of  the  left  hand  on  the  hole 
nearest  the  mouth  hole  and  the  next  two  holes,  the  fingers  of  the  right 
hand  on  the  other  four  holes.  Blow  across  the  mouth  hole,  lifting  first  one 
finger,  then  another,  off  the  holes.  The  notes  rendered  should  be  those  of 
the  scale  if  you  have  located  the  holes  accurately. 

The  echo. — Sound  may  be  reflected  from  a  surface  like  a  hillside  or 
the  wall  of  a  room  as  light  is  reflected  from  a  mirror.  Such  reflection 
out  of  door  gives  the  echo.  236.  Try  reflecting  sound  and  focusing  it 
with  a  mirror  like  that  used  on  bracket  lamps.  Hold  a  watch  a  few  inches 
in  front  of  the  mirror  that  is  held  so  as  to  reflect  the  sound  toward  a  second 
person.  Hold  a  candle  beside  the  watch  and  focus  the  light  on  the  person's 
ear.  The  sound  should  also  be  focused  and  the  person  will  hear  the  watch 
r  tick  with  concentrated  loudness.  Hold  your  hands  up  behind  your  ears, 
curving  the  hands  so  as  to  focus  the  sound  waves  into  the  openings  of  the 
ears.  Let  someone  talk  in  a  uniform  voice  while  you  do  this,  then  take 
your  hands  away.  Why  do  partially  deaf  people'use  an  ear  trumpet? 

The  string  telephone. — -237.  Punch  a  small  hole  in  the  middle  of  the 
bottom  of  two  tin  cans,  like  baking-powder  cans.  Fasten  one  end  of  a 
long  (50  feet  or  more)  heavy  string  in  each  can  by  passing  the  end  in  through 
the  hole  and  tying  a  knot  so  that  the  string  will  not  pull  out.  Let  each  of 
two  persons  hold  a  can  in  hand  and  stand  far  enough  apart  so  that  the 
string  is  pulled  taut.  Then  one  may  talk  into  the  can  and  the  other  use 
the  can  as  a  telephone  receiver.  If  two  lamp  chimneys  are  used  in  place 
of  the  cans,  one  end  of  each  being  covered  by  tightly  stretched  bladder  or 


g6  GUIDE  IN  PHYSICAL  NATURE-STUDY 

parchment  paper,  the  results  will  be  better.  The  string  may  turn  corners 
and  still  carry  the  sound,  if  it  is  passed  through  empty  spools  that  are 
suspended  from  convenient  objects.  You  can  thus  connect  two  rooms  in 
the  house  or  two  houses  that  are  not  too  far  apart. 

The  electric  telephone. — 238.  Examine  the  parts  of  an  old  telephone. 
Bear  in  mind  what  we  found  out  in  handling*  induced  electric  currents 
(P-  77)>  that  moving  a  magnet  into  or  out  of  a  coil  of  wire  produces  a 
current  in  the  wire.  Changing  the  strength  of  the  magnet  in  a  coil  will 
of  course  have  the  same  effect.  239.  After  looking  over  the  telephone 
and  finding  out  how  it  works,  could  you  devise  a  plan  of  making  one  for 
yourself  ?  Try  it. 


HOW  TO  MAKE  A  PAIR  OF  SCALES  AND  USE  OTHER 
MECHANICAL  CONTRIVANCES 

To  make  a  pair  of  balances. — 240.  Cut  a  block  of  J-inch  wood  4 
inches  square,  to  serve  as  a  base.  At  its  midpoint  fasten  an  8-inch  upright 
of  the  same  stuff  ij  inches  wide.  Saw  or  shave  off  the  sides  at  its  upper 
end  so  as  to  make  a  wedge  with  a  i^-inch  edge.  Cut  a  J-inch  square 
piece  15  inches  long  and  drive  a  tack  two-thirds  to  the  head  in  the  center 
of  each  end.  At  the  midpoint  of  this  piece  cut  a  notch  straight  across 
one  side  and  balance  the  stick  on  the  upright,  the  edge  of  the  wedge  in 
the  notch.  The  scale  pans  may  be  made  of  the  covers  of  baking-powder 
or  similar  cans.  Punch  three  holes  in  the  edge  of  each  cover  at  intervals 
of  a  third  of  the  way  around  the  cover.  Tie  short  strings  in  these  holes 
and  knot  their  ends  together  so  that  the  covers  will  hang  from  the  tacks 
at  each  end  of  the  balanced  stick.  If  now  the  stick  does  not  balance 
exactly,  shave  off  one  end  or  the  other  so  that  it  will.  At  the  midpoint 
of  the  balanced  stick  opposite  the  notch  fasten  an  8-inch  wire  by  a  tack, 
then  bend  it  an  inch  from  the  tack  so  that  it  will  hang  vertically  in  front 
of  the  upright.  Make  a  mark  upon  the  upright  at  the  lower  end  of  the 
wire  when  the  scale  beam  is  horizontal.  The  end  of  this  pointer  and  the 
mark  should  coincide  when  the  scale  pans  just  balance. 

241.  To  make  the  weights,  take  a  pound  of  sheet  lead  and  cut  it  in 
half.  Cut  one-half  in  half  again,  and  so  proceed  to  make  weights  of  8-ounce, 
4-ounce,  2-ounce,  i-ounce,  and  two  J-ounce;  weights  may  be  made  also,  if 
preferred,  by  using  small  cloth  bags  filled  with  small  shot,  weighing  them 
on  some  reliable  scales.  Such  scales  and  weights  will  make  a  valuable 
addition  to  the  outfit  of  the  boy  or  girl  who  wants  to  play  store. 

An  experiment  with  the  scales. — '242.  Make  another  notch  on  the 
scale  beam  on  the  same  side  as  before,  but  5  inches  from  one  end.  Set 
the  beam  on  the  upright  at  this  notch  and  pour  fine  shot  into  one  scale 
pan  until  the  scales  balance.  If  the  2-ounce  weight  is  now  put  in  the  pan 
with  the  shot,  what  weight  must  be  put  in  the  other  pan  to  balance  it? 
Try  the  4-ounce  weight  and  note  what  is  required  to  balance  it.  What  is 
the  relation  between  the  weights  in  the  two  pans  in  each  case?  What  is 
the  relation  between  the  lengths  of  the  arms  of  the  scale  beam  now? 

243.  Cut  another  notch  3  inches  from  one  end  and  again  get  the 
scales  balanced  by  pouring  shot  in  one  pan.  Put  the  2-ounce  weight  in 
this  pan  again  and  note  what  weight  is  needed  in  the  other  pan  to  balance 

97 


g8  GUIDE  IN  PHYSICAL  NATURE-STUDY 

it.  The  number  representing  the  weight  in  one  pan  multiplied  by  that 
showing  the  length  of  the  opposite  arm  always  equals  what?  244.  Devise 
and  make  a  pair  of  scales  on  which  you  can  weigh  yourself. 

The  lever. — The  balance  is  merely  one  form  of  the  simple  machine 
called  a  lever.  The  unmoved  point  upon  which  the  beam  balances  is 
the  fulcrum.  One  arm  is  called  the  weight  arm,  the  other  the  power 
arm,  because  they  bear,  respectively,  the  weight  and  the  power.  We  may 
state  our  findings  above,  then,  in  this  form:  weight  arm  times  the  power 
equals  what? 

There  are  evidently  only  three  possible  relations  of  fulcrum,  weight, 
and  power.  The  fulcrum  may  be  between  the  weight  and  power;  the 
weight  may  be  between  the  fulcrum  and  power;  power  may  be  between 
fulcrum  and  weight. 

There  are  many  applications  of  the  lever,  as,  for  instance,  a  hammer 
used  for  drawing  a  nail,  a  tack  claw,  a  can  opener,  scissors  used  in  cutting, 
a  nut  cracker,  a  lemon  squeezer.  245.  Draw  diagrams  of  each  of  these 
indicating  the  location  of  fulcrum,  power,  and  weight.  246.  List  some 
other  common  household  utensils  that  involve  the  use  of  a  lever. 

247.  Fasten  a  spring  scale  to  the  end  of  a  hammer  handle.  Insert 
the  hook  of  a  second  spring  scale  in  the  claw  of  the  hammer.  Set  the 
hammer  head  down  at  the  edge  of  a  table  and  take  hold  of  one  spring 
scale  with  the  right  hand,  the  other  with  the  left.  Pull  on  the  scale  attached 
to  the  handle  as  if  the  other  spring  scale  were  a  tack  you  were  drawing. 
Note  what  each  spring  scale  registers.  Measure  the  weight  arm  and  power 
arm  of  this  lever  and  note  if  the  amounts  registered  by  the  spring  scales 
figure  out  properly  in  relation  to  the  length  of  power  arm  and  weight  arm. 

The  sprocket  wheel  on  the  bicycle.— 248.  Cut  a  piece  of  |-inch  stuff 
2  inches  wide  and  2  inches  long  for  a  base.  At  one  end  fasten  on  with 
brads  two  uprights,  one  on  each  side,  each  upright  of  light  stuff  and  about 
i  inch  by  3  inches,  the  two  parallel  to  each  other  and  at  right  angles  to 
one  broad  side  of  the  base.  Whittle  a  4-inch  stick  round  and  sufficiently 
large  to  tightly  fit  the  hole  in  a  spool.  Bore  a  hole  a  little  larger  than  this 
round  stick  in  each  of  the  uprights  near  their  upper  ends  so  that  the  round 
stick  can  set  in  them  and  turn  as  an  axle,  the  spool  turning  with  it.  Square 
off  one  protruding  end  of  the  axle  and  at  right  angles  fit  on  it  an  arm  of 
light  wood  with  a  square  hole  at  one  end  to  receive  the  square  end  of 
the  axle.  At  the  other  end  of  the  arm,  which  may  be  a  couple  of  inches 
long,  drive  a  peg  into  a  small  hole  to  make  the  handle  to  this  crank  on  the 
windlass.  The  crank  is  like  the  pedal  bar  on  the  bicycle,  the  spool  compa- 
rable to  the  sprocket  wheel.  Let  us  see  what  mechanical  advantage  such 
a  mechanism  affords.  Tie  one  end  of  a  string  tightly  around  the  spool  and 


HOW  TO  MAKE  MECHANICAL  CONTRIVANCES  99 

then,  turning  the  handle  of  the  windlass,  wind  several  turns  of  the  string 
upon  the  spool.  Tie  the  free  end  of  the  string  to  the  hook  of  a  spring  scale, 
the  other  end  of  which  is  fastened  to  a  tack  on  the  table.  Fasten  the  base 
block  to  the  tablfe  also.  Throw  the  hook  of  another  spring  scale  over  the 
handle  of  the  crank  and  by  means  of  it  apply  force  to  turn  the  crank. 
As  you  thus  wind  the  string  slowly  on  the  spool  note  the  reading  of  both 
scales.  Then  let  the  string  unwind  a  very  little  and  again  note  the  reading 
of  both  scales.  *  If  you  divide  the  sum  of  the  readings  of  each  scale  by  two 
the  results  should  be  the  force  applied  on  the  crank  to  pull  a  given  weight 
on  the  string;  the  element  of  friction  is  also  eliminated.  Do  you  know 
why? 

Do  you  see  also  that  this  machine  is  merely  an  application  of  the  lever? 
What  is  the  power  arm,  the  weight  arm?  Are  these  constantly  changing 
their  relative  lengths  as  the  windlass  is  turned,  or  do  they  remain  constant? 
Measure  these  arms  of  the  lever  and  calculate  to  see  how  closely  your 
measure  of  the  force  applied  and  the  resistance  overcome  agrees  with  the 
amounts  determined  from  the  application  of  the  law  of  the  lever. 

Bearing  down  with  a  pressure  of  twenty  pounds  on  the  pedal  of  your 
bicycle  what  pull  is  given  on  the  chain  by  the  teeth  of  the  sprocket  wheel? 

There  is  such  a  crank  and  axle  on  the  coffee  mill,  the  wringer,  and  the 
ice-cream  freezer.  249.  Can  you  figure  out  in  either  of  these  how  much 
the  power  applied  to  the  crank  handle  is  multiplied  by  the  machine? 

Wheel  and  axle  on  the  sewing  machine. — If  the  crank  on  the  end  of 
the  axle  is  replaced  by  a  wheel  the  machine  is  known  as  a  wheel  and  axle. 
But  the  principle  involved  is  merely  that  of  the  lever  again,  for,  of  course, 
when  the  crank  handle  on  the  windlass  is  turned  around  it  describes  the 
circumference  of  a  circle  just  as  does  the  rim  of  a  wheel.  The  steering 
wheel  of  a  boat  works  as  a  wheel  and  axle.  Are  there  any  on  the  sewing 
machine?  Can  you  think  of  any  others  in  common  use? 

To  make  a  pulley. — 250.  Cut  two  thin  wood  strips  from  a  cigar  box 
each  ij  inches  by  |  inch.  Bore  a  hole  in  the  center  of  each  through 
which  may  be  set  an  axle  on  which  revolves  an  empty  silk  spool.  With 
small  brads  fasten  a  block  of  wood  in  each  end  thick  enough  for  the  spool 
to  revolve  freely.  Fasten  in  each  end  of  this  pulley  a  small  screw  hook  or 
a  brad  bent  into  a  hook. 

Why  pulleys  can  help  lift  a  load. — 251.  Fasten  up  a  single  pulley, 
pass  a  string  over  the  wheel  and  tie  one  end  to  the  hook  of  a  spring  scale 
and  a  weight  of  8  ounces  to  the  other  end.  What  does  the  spring  scale 
register?  What  would  be  the  advantage  in  using  such  a  pulley  then?  Can 
you  determine  how  much  of  the  pull  exerted  by  the  scale  in  raising  the 
weight  is  used  up  in  overcoming  friction? 


ioo  GUIDE  IN  PHYSICAL  NATURE-STUDY 

252.  Fasten  one  end  of  the  string  to  the  bottom  of  the  pulley,  already 
hung,  from  which  the  string  has  been  removed,  pass  the  string  over  the 
wheel  of  a  second  pulley  so  as  to  suspend  it  below  the  first,  thence  over 
the  wheel  of  the  first.     Fasten  the  hook  of  a  spring  scale  to  the  free  end  of 
the  string  and  hang  a  half-pound  weight  on  the  hook  of  the  lower  pulley. 
See  what  the  spring  scale  registers.    What  should  it  register  if  friction  were 
eliminated?     Can  you  devise  a  way  to  eliminate  friction  in  your  results? 
How  many  strings  are  now  supporting  the  weight?    If  you  raise  the  weight 
6  inches  how  much  must  you  lower  the  end  of  the  string  fastened  to  the 
spring  scale?    Make  the  measurement  to  find  out. 

253.  Try  a  system  of  a  double  pulley  above  and  a  single  pulley  below. 
Fasten  the  end  of  the  string  to  the  upper  end  of  the  lower  pulley,  pass 
it  over  one  of  the  wheels  of   the  upper  pulley,  then  over  the  wheel  of 
the  lower  pulley,  then  over  the  other  wheel  of  the  upper  pulley.    Fasten  the 
hook  of  the  spring  scale  to  the  free  end  of  the  string  and  a  weight  to  the 
lower  hook  of  the  lower  pulley.    See  what  the  relation  is  between  the  weight 
raised  and  the  power  required  to  raise  it  after  making  allowance  for  friction. 
254.  Try  a  system  of  two  double  pulleys  and  find  out  the  same  thing. 
Do  you  see  any  relation  between  the  weight  raised,  the  power  applied, 
and  the  number  of  strands  of  cord  that  support  the  weight,  remembering 
that  one  strand  of  string  merely  serves  to  change  the  direction  of  the  applied 
power,  as  in  the  single  pulley.    Would  it  be  possible  for  a  man  to  lift  him- 
self with  a  rope  and  a  couple  of  pulleys? 

Why  the  grocer  uses  an  inclined  plank  to  load  the  barrel  of  sugar  into 
his  wagon.  255.  Cut  a  small  block  of  f-inch  wood  3  inches  wide  and 
4  inches  long.  At  the  middle  of  one  end  drive  a  tack.  By  means  of  nails 
fasten  four  small  spools  to  the  block  to  serve  as  wheels,  thus  making  a 
small  wagon.  Fasten  a  string  to  the  block  by  means  of  the  tack  at  the 
front  end.  Load  the  wagon  with  some  weights  and  then  by  means  of  a 
spring  scale  attached  to  the  string  weigh  the  wagon  and  its  load. 

Support  one  end  of  a  smooth  5-foot  board  on  blocks  so  that  it  is  3  feet 
higher  than  the  other  end,  which  rests  on  the  table  or  the  floor.  Draw  the 
wagon  up  the  inclined  board  and  note  the  pull  registered  on  the  spring 
scale.  Note  the  pull  on  the  scales  when  the  wagon  is  allowed  to  roll,  back- 
ward, down  the  inclined  board.  In  pulling  the  wagon  up  the  board  the 
scale  registers  the  pull  of  the  wagon  plus  the  resistance  due  to  friction  of 
the  wheels;  when  the  wagon  rolls  back  the  scale  registers  the  pull  of  the 
wagon  minus  the  friction.  How,  then,  will  you  get  the  pull  due  to  the 
loaded  wagon  and  eliminate  the  element  of  friction?  What  is  this  amount? 
How  far  has  the  weighted  wagon  to  move  horizontally  in  going  from  one 
end  of  the  board  to  the  other?  How  far  must  it  move  vertically?  If  the 


HOW  TO  MAKE  MECHANICAL  CONTRIVANCES      101 

wagon  and  its  weight  equaled  one  pound  and  it  were  lifted  directly  from 
the  table  or  floor  to  the  raised  end  of  the  board  the  energy  used  would 
evidently  be  three  foot  pounds.  What  energy  was  used  in  raising  the  wagon 
in  the  experiment?  The  pull  registered  on  the  scale,  leaving  friction  out 
of  consideration,  is  what  part  of  the  weight  of  the  loaded  wagon?  But 
this  pull  was  working  through  how  many  horizontal  feet  of  movement  of 
the  wagon?  Do  you  see  that  the  proportion  existing  between  the  weight 
raised  and  the  pull  on  the  scale  is  the  same  as  that  between  the  vertical 
distance  and  the  horizontal  distance  through  which  the  weight  moves? 
Can  you  explain  why  this  is  so?  256.  Suppose  the  end  of  the  board 
were  raised  2  feet  instead  of  3  feet,  then  what  would  be  the  pull  on  the 
scale  required  to  get  the  wagon  up  the  inclined  board?  Figure  this  out 
first  and  then  verify  your  conclusion  by  trying  the  experiment.  Can  you 
now  state  the  law  of  the  inclined  plane?  Would  the  grocer  best  use  a  long 
or  a  short  board  to  roll  his  barrel  of  sugar  up  into  the  wagon?  When  a 
railroad  goes  up  a  mountain  why  must  it  wind  back  and  forth  around 
the  mountain?  The  grade  must  not  exceed  2  per  cent  if  an  engine  is  to 
pull  a  train  of  cars.  What  does  such  a  statement  mean?  Why  must  the 
gradient  be  so  small?  Why  is  it  so  hard  to  ride  a  bicycle  up  a  hill? 

Why  a  knife  blade  cuts  so  easily. — Do  you  see  that  a  knife  blade  is 
just  another  application  of  the  machine  called  the  inclined  plane?  Instead 
of  pulling  the  weight  up  the  inclined  plane  the  plane  is  forced  in  against 
the  resistance  caused  by  the  cohesion  of  the  particles  of  wood  or  other 
object  cut.  Though  this  simple  machine  is  simply  a  new  application  of 
the  old  inclined  plane  it  is  called  the  wedge.  257.  Can  you  measure  your 
knife  blade  and  calculate  what  amount  of  force  is  acting  to  push  the  wood 
fibers  apart  if  you  are  exerting  a  pressure  of  five  pounds  on  the  handle  of 
the  knife?  Name  five  other  tools  that  use  the  wedge  as  a  means  of  accom- 
plishing their  work. 

Why  even  a  child  can  raise  an  automibile  with  a  jack. — 258.  Cut  a 
long  right  triangle  out  of  paper,  making  one  side  of  the  right  angle 
6  inches,  the  other,  i  inch.  Lay  the  i-inch  end  on  a  pencil  parallel  to  its 
length  and  roll  the  paper  strip  on  the  pencil.  The  longest  side  of  the  triangle, 
the  hypotenuse,  makes  a  spiral  like  a  screw  thread.  It  is  evident,  then, 
that  the  screw,  another  simple  type  of  machine,  is  really  only  an  applica- 
tion of  the  principle  of  the  inclined  plane,  for  the  longest  side  of  the  tri- 
angle is  comparable  to  the  edge  of  an  inclined  plane.  The  screw,  then,  is 
merely  a  coiled  inclined  plane  and  of  course  works  in  the  same  manner. 
The  power  applied  to  a  screw  jack  is  also  usually  applied  by  means  of  a 
long  handle  that  acts  as  a  lever  to  further  increase  the  efficiency  of  the 
machine. 


102  GUIDE  IN  PHYSICAL  NATURE-STUDY 

If  we  take  a  coarse  wooden  screw,  like  that  on  a  carpenter's  bench  vise, 
it  will  be  easy  to  measure  the  elements  in  the  inclined  plane.  259.  With 
a  tapeline  measure  the  circumference  of  the  screw.  Evidently  when  the 
handle  of  the  vise  is  turned  around  once,  the  resistance,  whatever  it  is, 
has  moved  horizontally  over  a  distance  equal  to  that  measured.  It  has 
at  the  same  time  moved  vertically,  to  adopt  the  same  phrasing  as  used 
above  for  the  inclined  plane,  a  distance  equal  to  that  between  correspond- 
ing points  on  successive  turns  of  the  screw.  Measure  this  distance.  We 
now  have  the  two  essential  elements  in  an  inclined  plane.  What  should 
be  the  increase  in  power  accomplished  through  the  use  of  this  screw? 
Probably  the  bench  screw  operates  by  means  of  a  handle  that  acts  as  a 
lever  to  further  increase  the  power.  Measure  the  length  of  power  arm 
and  weight  arm  and  calculate  what  its  mechanical  efficiency  is. 

We  may  experimentally  verify  our  calculations.  260.  Cut  two  sticks 
of  J-inch  stuff  an  inch  or  so  wide  and  fasten  them  together  loosely  by 
a  nail  or  bolt  set  through  them  at  their  midpoints,  thus  making  a  crude 
pair  of  shears.  Bore  holes  through  the  ends  of  the  sticks  that  may  be 
called  the  tips  of  the  shears.  Fasten  the  other  ends  of  the  sticks,  the  handles 
of  the  shears,  to  the  jaws  of  the  bench  vise  by  means  of  brads,  so  that  when 
the  vise  is  opened  by  turning  the  screw  the  tips  of  the  shears  will  be  spread. 
Fasten  a  spring  scale  between  these  tips  by  strings  tied  in  the  holes.  Hook 
another  spring  scale  over  the  handle  of  the  bench  vise  and  turn  the  screw 
so  as  to  open  the  shears.  Note  the  reading  on  both  scales.  Is  the  power 
applied  increased  by  the  machine  as  much  as  you  calculate  it  should  be? 
If  not,  why  not? 


APPENDIX  A 

It  is  suggested  that  the  following  list  of  projects,  outlined  in  the  pre- 
ceding pages,  be  done  by  individual  students  or  the  instructor  as  class 
demonstrations  and  that  all  others  be  done  by  every  student  in  the 
class:  21,  42,  44,  48,  52,  57,  58,  60,  61,  63,  64,  65,  72,  73,  74,  75,  76,  80, 
81,  85,  87,  92,  93,  96,  98,  100,  lor,  102,  105,  106,  107,  108,  no,  in,  113, 
114,  116,  117,  118,  119,  120,  121,  124,  125,  127,  128,  130,  133,  144,  146, 
147,  149,  151,  152,  168,  169,  170,  174,  178,  179,  180,  185,  194,  200,  202, 

203,    214,    222,    223,    232,    233,    234,    235,    237,    239,    240,    241,    242,    243,   244, 

248, 255, 260. 


103 


APPENDIX  B 

The  following  list  of  apparatus  and  supplies  is  required  to  work  out 
the  projects  suggested  in  this  book,  the  foregoing  list  of  experiments  to 
be  performed  by  one  member  of  the  class  for  the  benefit  of  all.  The 
estimate  is  based  on  a  class  of  twenty  students.  It  does  not  include 
drawing  material,  extra  paper,  cardboard,  etc.,  that  would  naturally 
be  supplied  by  the  pupils. 

Alcohol  lamps  or  Bunsen  burners,  10. 
Asbestos  paper,  thin,  i  sq.  ft. 
Asbestos  sheet,  -rV  in.,  2  sq.  yds. 
Bamboo  poles,  2. 

Beads,  2  doz.,  J  in.  with  large  hole. 
Beakers,  500  c.c.,  6. 
Bolts,  3  by  |  in.,  20. 
Bottles,  8-oz.,  wide-mouthed,  6. 
Brads,  f  lb.,  \  in. 
\  lb.,  f  in. 
i  lb.,  1 1  in. 

Bunsen  burners  or  alcohol  lamps,  10. 
Candles,  2  standard. 
Cheese  cloth,  5  yds. 
Chemicals: 

Acid  chlorhydric,  8  oz. 

Alcohol,  4  oz.  (more  if  alcohol  lamps  are  used). 

Alum,  \  lb. 

Ammonium  chloride,  4  oz. 

Calcium  oxide,  |  lb. 

Camphor,  2  oz. 

Carmine,  powdered,  \  oz. 

Charcoal,  pulverized,  4  oz. 

Copper  sulphate,  8  oz. 

Ether,  2  oz. 

Magnesium  ribbon,  i  oz. 
.  Manganese  dioxide,  granular,  4  oz.;  pulverized,  4  oz. 

Phosphorus,  yellow,  2  oz. 

Potassium  chlorate,  4  oz. 

Salt,  coarse,  i  lb. 

Silver  nitrate,  \  oz. 

Sulphur,  8  oz. 

Turpentine,  4  oz. 

Zinc,  granulated,  4  oz. 
Clay  pipes,  3. 
Compasses,  10. 

104 


APPENDIX  105 


Compression  clamps,  4. 
Copper,  sheet,  i  sq.  ft. 

Corks,  rubber,  to  fit  flasks  2-holed  and  10  small  i -holed. 
Corks,  assorted  sizes,  50. 
Electric  bell. 

Electric  binding-posts  with  two  openings,  4. 
Electric  buzzer. 
Electric  dry  batteries,  10. 
Electric  dynamo,  toy. 
Electric  knife  switch. 
Electric  lights,  old  incandescent. 
Electric  lights,  i-candle  power,  and  sockets,  20. 
Electric  motor,  toy. 
Electric  push  button. 
Evaporating  dishes,  5  of  100  c.c. 
Flasks,  3  of  2  liters. 
5  of  f  liter. 
20  of  100  c.c. 

Filter  paper,  i  package,  5  in.  diameter. 
Funnels,  2  of  i  in.  diameter, 

2  of  3  in.  diameter. 
Gas  engine,  toy. 
Glass  cutter,  wheel,  2. 
Glass  stirring  rods,  i  dozen. 
Glass  tubing,  i  Ib.  soft,  iVin.  bore. 
i  Ib.,  j-in.  bore. 
5  of  6-in.  length,  |-in.  bore. 
5  of  4-in.  length,  i-in.  bore. 
Glass,  window,  3  pieces  8  by  10. 
Gunnysack,  i. 

Iron,  round,  -&•  in.,  10  linear  ft. 
Joss  sticks,  i  package. 
Knitting  needles,  10  steel. 
Lamp  chimneys,  2. 
Lead,  sheet,  i  sq.  ft. 
Leather,  i  sq.  ft.,  thin. 
Lemon  squeezer. 
Level,  2  detached. 
Lumber,  10  linear  ft.,  f  in.,  3  in.  wide,  white  pine. 

10  linear  ft.,  f  in.,  9  in.  wide,  white  pine. 

10  linear  ft.,  \  in.,  9  in.,  white  pine. 

30  |-in.  square  strips,  3  ft.  long,  white  pine. 

20  |-in.  square  strips,  4  ft.  long,  oak  or  cedar. 
Magnets,  bar,  10. 
Mica,  i  piece,  2  in.  square. 
Minerals  and  rocks  (specimens  listed,  p.  6). 


io6  GUIDE  IN  PHYSICAL  NATURE-STUDY 

Mirrors,  10  pieces  6  in.  square. 
10  concave. 

40  strips  about  i  by  6  in. 
Nails,  assorted  wire,  2  Ibs. 
Nut  cracker. 

Paper,  colored,  i  package  assorted  colors,  about  2  doz.  sheets. 
Paper,  tissue,  40  sheets,  assorted  colors. 
Phonograph  record,  2  old,  i  good  one. 
Photograph  material: 

Blueprint  paper,  5  by  8,  2  doz.  sheets. 
4  by  5,  2  doz.  sheets. 

Fixer,  acid,  i  Ib. 

Hyjdrochinone  developer,  6  powders. 

Metol-hydrochinone  developer,  3  tubes. 

Plates,  i  box,  4  by  5,  Cramer's  medium  or  equivalent. 

Print  paper,  2  doz.  sheets  4  by  5  Normal  Cyko  or  equivalent. 
Picture  cord,  i  package. 
Pie  plates,  tin,  2. 
Pipettes,  i  doz.  straight. 
Pith  balls,  20. 
Plasticine,  i  Ib. 
Pneumatic  trough. 
Prism,  2-in.,  2. 

Protractor,  3-in.,  brass  or  horn. 
Ring  stands,  2. 
Rubber  for  aeroplane,  40  ft. 
Rubber  bands,  2  doz.,  2  in. 

Rubber  tubing,  10  ft.,  to  fit  glass  tubing  of  iVin.  bore. 
Saucers,  10. 

Scales,  spring,  8  oz.,  20, 
Scales,  spring,  2  Ib.,  2. 
Sealing  wax,  10  sticks. 
Shot,  i  Ib. 

Silk,  several  pieces  large  enough  to  rub  glass  tubing. 
Silk,  i  spool  fine. 
Spikes,  i  doz. 
String,  5  balls. 

Surgeons'  tape,  i  in.  wide,  10  yds. 

Tacks,  i  package  each,  small,  carpet,  and  double-pointed. 
Teapot,  i  small  tin. 
Telegraph  instruments,  2. 
Telephone,  i  old  one. 
Test  tubes,  20. 

Thermometers,  3  registering  — 10°  to  220°  F.,  or  equivalent  in  C. 
Thermos  bottle — broken  one  is  best. 


APPENDIX  107 

/ 

Tin  foil,  4  oz. 
Tin,  sheet,  i  sq.  ft. 
Tools: 

5  awls. 

5  triangular  files. 

2  round  files. 

10  hammers. 

20  knives,  Sloyd. 

5  pliers. 

2  saws,  cross,  and  i  split,  i  keyhole,  i  hack. 
10  pairs  scissors. 

5  screw  drivers. 

i  pair  tinners'  shears. 

i  bench  vise.  •• 

Tumblers,  20. 
Voltammeter,  i. 
Watch  crystals,  not  the  laboratory  dishes  of  this  name  but  real  watch  crystals, 

3  doz. 

Wire,  No.  12,  soft-iron,  2  Ib. 

iron,  1 8  and  24,  i  spool  each. 
*       copper,  1 8  and  24,  i  spool  each. 

copper  insulated,  18,  f  Ib. 

copper  insulated,  36,  i  Ib. 
Zinc,  sheet,  i  sq.  ft. 


APPENDIX  C 

There  is  given  herewith  a  brief  list  of  books  that  will  be  found  useful 
if  it  is  desired  to  extend  the  list  of  projects  to  be  carried  out  by  the  pupils. 
A  more  complete  bibliography  will  be  found  at  the  ends  of  the  chapters 
in  the  forthcoming  Source  Book  of  Physical  Nature-Study,  which  it  is 
intended  shall  serve  as  a  reading  text  to  accompany  this  laboratory  and 
field  guide. 

Bayley,  W.  S.    Minerals  and  Rocks.    New  York:   D.  Appleton  &   Co.,    1915. 

$2 . OO . 

Beard,  Dan  C.     The  American  Boy's  Handybook.    New  York:   Charles  Scribner 

&  Sons,  1914.     $1.50. 

.    Boat-Building  and  Boating.  '  New  York:   Grosset,  Dunlap  &  Co.,  1914. 

$0.50. 

.    Handicraft  for  Outdoor  Boys.    New  York:   Grosset,  Dunlap  &  Co.,  1915. 

$0.50. 
Bond,  Alexander  R.     The  Scientific  American  Boy.    New  York:   Munn  &  Co., 

1905.    $1.50. 
Chadwick,  M.  L.  Pratt.    Storyland  of  Stars.     Chicago:   Educational  Publishing 

Co.,  1906.    $0.50. 
Collins,  Archie  F.    Easy  Lessons  in  Wireless.    New  York:  Theo.  Audel  &  Co., 

1915.    $0.50. 
Collins,  Francis  A.     The  Boyjs  Book  of  Model  Aeroplanes.    New  York:  The 

Century  Co.,  1910.     $i .  20. 
Crosby,  W.  O.     Common  Minerals  and  Rocks.     Boston:   D.  C.  Heath  &  Co., 

1881.     $0.64. 

Fairbanks,  H.  W.    Stories  of  Rocks  and  Minerals.     Chicago:   Educational  Pub- 
lishing Co . ,  1 903 .    $o . 60 . 
Griffith,  Alice  M.     The  Stars  and  Their  Stories.    New  York:  Henry  Holt  &  Co., 

1-913.    $1.25. 
Hall,  A.  N.    Homemade  Toys  for  Boys  and  Girls.     Boston:   Lothrop,  Lee  & 

Shepherd,  1915.     $1.35. 

.    Handicraft  for  Handy  Boys.     Boston:  Lothrop,  Lee  &  Shepherd,  1911. 

$2.00. 
Hobbs,  W.  H.    Simple  Directions  for  the  Determination  of  the  Common  Minerals 

and  Rocks.    New  York:   The  Macmillan  Co.,  1914.    $o.  25 . 
Hopkins,  George  M.    Experimental  Science.     New  York:   Munn   &  Co.,  1906. 

$7.00. 
Hubbard  and  Turner.      The  Boys'  Book   of  Aeroplanes.     New  York:    F.  A. 

Stokes  &  Co.,  1913.     $i..75. 

108 


APPENDIX  109 

Johnson,  G.  F.     Toys  and  Toy  Making.    New  York:   Longmans,  Green  &  Co., 

1912.    $1.00. 
Olcott,  William  T.    Star  Lore  of  All   the  Ages.    New  York:   G.  P.  Putnam's 

Sons,  1911.    $3.50. 

— .    A  Field  book  of  the  Stars.    New  York:  G.  P.  Putnam's  Sons,  1907. 

$1.00. 
Porter,  J.  G.     The  Stars  in  Song  and  Legend.    Boston:    Ginn   &   Co.,   1901. 

$0.50. 
Proctor,  Richard  A.    Myths  and  Marvels  of  Astronomy.    New  York:  Longmans, 

Green  &  Co.,  $1.75. 
.    Stars  in  Their  Season.     New  York:   Longmans,  Green  &  Co.,  1907. 

$2.00. 

Rowe,  J.  P.    Practical    Mineralogy,    Simplified.    New  York:   John    Wiley   & 

Sons,  1911.     $i  .25. 
St.  John,  Thomas  M.    Real  Electric  Toy  Making  for  Boys.    New  York:   Thomas 

M.  St.  John,  1911.     $1.00. 
Serviss,  Garrett  P.    Astronomy  with  the  Naked  Eye.    New  York:  Harper  Bros., 

1008.    $1.40. 

.    Round  the  Year  with  the  Stars.    New  York:  Harper  Bros.,  1910.    $i .  oo . 

Sloane,  Thomas  0.    Electric  Toy  Making  for  Amateurs.    New  York:   Norman 

W.  Henley  Publishing  Co.,  1914.    $i  .00. 
Spencer,  L.  J.     World's  Minerals.    New  York:  F.  A.  Stokes  &  Co.,  1916.    $2.75. 


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